Method and apparatus for digital watermarking

ABSTRACT

A method for embedding digital watermark data in digital data contents includes the steps of obtaining a frequency coefficient of block data of digital data contents, obtaining a complexity of the block data, obtaining an amount of transformation of the frequency coefficient from the complexity and the digital watermark data, and embedding the digital watermark data by transforming the frequency coefficient. In addition, a method for reading digital watermark data includes the steps of calculating a probability of reading ‘1’ or ‘0’ in a read bit sequence by using a test method on the basis of binary distribution, determining the presence or absence of digital watermark data according to the probability, and reconstituting digital watermark data. Another method includes the steps of performing soft decision in code theory by assigning weights to the digital watermark sequence with a weighting function, and reconstituting digital watermark data.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to a digital watermarkingtechnique. More particularly, the present invention relates to a digitalwatermarking technique for embedding or reading digital watermark datain digital data contents which represent an image or a sound. Inaddition, the present invention relates to a technique for statisticalprocessing of read watermark data in a system using the digitalwatermarking technique.

[0003] It is easy to replicate or tamper fraudulently with multimediaproduction, and the easiness hinders an data content provider fromsending data. In addition, some users may not use the data originatedfrom the provider validly. Therefore, copyright protection is stronglyneeded for the multimedia production. The digital watermarking techniqueis effective in realizing the copyright protection. According to thedigital watermarking technique, sub-data is embedded in data contentswithout being noticed by a user by utilizing redundancy of data such asof an image and a sound. The digital watermarking technique is used forprotecting a multimedia copyright by embedding copyright information, auser ID and the like as the sub-data in secret, since it is difficult toseparate the sub-data from the data contents.

[0004] 2. Description of the Related Art

[0005] Conventionally, the following digital watermarking techniques areproposed.

[0006] According to a technique proposed in Japanese patent applicationNo.9-57516, “Image processing method and the apparatus,” an image issubdivided into blocks larger than a 8×8 block size which is used forcommon non reversible compression. Then, the size of the frequencycoefficient which is obtained by discrete Fourier transform of the blockis changed, the frequency coefficient being represented by a polarcoordinate system and the size being a distance from the origin point ofthe polar coordinate system. As a result, sub-data can be read correctlyeven when the non-reversible compression is performed. In addition, thefrequency coefficient is normalized within a range of predeterminedvalues, is embedded, and read. In addition, weaker image processing iscarried out on a complicated region as compared to a flat region. As aresult, degradation of image quality which may be caused by embeddingthe sub-data can be suppressed and a tolerance to contrast changing isobtained. Further, as the value of the frequency coefficient to bechanged becomes larger, the modification amount of the frequencycoefficient becomes larger (the smaller the value is, the smaller themodification amount is) so as to suppress the deterioration of imagequality more effectively. In addition, when subdividing an image intoblocks, an image area which is smaller than one block is treated as oneblock by using an average pixel value and/or using a form symmetric withrespect to a line repeatedly to compensate for the lacking image area.Moreover, the sub-data is constituted from the whole image afterweighting data of each block. As a result, the sub-data is readcorrectly even when the image is partly edited and/or the image withmany flat parts is non-reversibly compressed.

[0007] In addition, according to a technique proposed in Japanese patentapplication No.9-164466, “Information embedding method, data readingmethod and the apparatus,” when embedding data into motion pictures,data embedding is carried out to components of a relatively lowfrequency region. Further, frequency conversion is carried out with ablock size larger than a block size used for data compression, and, thendata embedding is carried out. Moreover, an original image is used whendata is read. As a result, tolerance to data compression is obtained.

[0008] Other conventional techniques are proposed in Japanese patentapplications No.8-305370, No.8-338769, No.9-9812, No.9-14388,No.9-109924, No.9-197003, No.9-218467 and No.10-33239. The digitalwatermark method is also called data hiding, finger printingsteganography, image/sound deep encryption and the like.

[0009] Elements for determining performance of the digital watermarkingtechnique are as follows:

[0010] (1) quality of data contents in which the digital watermark isembedded;

[0011] (2) durability of the digital watermark which is embedded in thedata contents when the data contents are manipulated;

[0012] (3) safety against intentional erasing of and tampering withdigital watermark data, and

[0013] (4) reliability of the digital watermark data which is read fromthe data contents.

[0014] The digital watermarking technique is broadly divided into twomethods. One method of gives meaning to a data value by quantizing. Forexample, by dividing a data value by a quantization value and dividingthe result by 2, a bit data can be represented by the remainder. Anothermethod embeds digital watermark data by using a spread spectrum method.

[0015] The above-mentioned examples are based on the former method. Interms of the method, there is a problem with respect to the aboveelement (1) in that the digital watermark data embedded in the datacontents may be perceived, or commercial value of the data contents maybe lost by embedding the digital watermark data. With respect to theabove element (2), the digital watermark data which is embedded in thedata contents may be dissipated even when a general user uses the datacontents in a normal way. Particularly, it is a difficult problem toachieve both elements (1) and (2) with enough performance in practicaluse.

[0016] In addition, there is a method of embedding the digital watermarkdata repeatedly in order to give durability to the digital watermarkdata against manipulation of the data contents. Specifically, accordingto the method, digital watermark data which is embedded repeatedly(which is called a watermark sequence hereinafter) is read from datacontents, and, then, the digital watermark data is reconstituted byperforming statistical processing. The watermark sequence has durabilityagainst deterioration and noise to some extent. However, if the datacontents are encoded by high compression rates, it may become difficultto read the watermark sequence from the data contents. Therefore, it maybecome impossible to reconstitute the digital watermark data.

[0017] In addition, as for a digital watermarking system, accuracy fordetermining the presence or absence of embedded data is important. Inaddition, reliability of embedded data is important. The digitalwatermarking system generally has a mechanism for reconstituting correctdigital watermark data even when sub-data embedded in the data contentsis corrupted to a certain extent, since the digital watermarking systemassumes various processing on the watermarked data contents. However,under present circumstances, it is impossible for the system to evaluatevalidity of reconstituted digital watermark data quantitatively.Therefore, the system does not have enough reliability.

SUMMARY OF THE INVENTION

[0018] It is a first object of the present invention to improve qualityof watermarked digital data contents and to improve durability ofdigital watermark data against media processing of the watermarkeddigital data contents.

[0019] It is a second object of the present invention to evaluatequantitatively probabilities of cases that data contents which do notcontain digital watermark data are wrongly judged as containing digitalwatermark data, and incorrect digital watermark data is read fromwatermarked digital data contents.

[0020] It is a third object of the present invention to separate adigital watermark data sequence, when reading watermarked digital datacontents, from noise so that error bits which are included in thedigital watermark data sequence can be reduced, thereby watermark datareading success rate being improved in comparison with the conventionalmethod without changing an amount of digital watermark data and a methodof embedding the digital watermark data.

[0021] The first object of the present invention is achieved by a methodfor embedding digital watermark data in digital data contents. Themethod includes the steps of:

[0022] receiving the digital data contents and the digital watermarkdata;

[0023] dividing the digital data contents into block data;

[0024] obtaining a frequency coefficient of the block data;

[0025] obtaining a complexity of the block data;

[0026] obtaining an amount of transformation of the frequencycoefficient from the complexity and the digital watermark data by usinga quantization width;

[0027] embedding the digital watermark data in said digital datacontents by transforming the frequency coefficient by the amount; and

[0028] generating watermarked digital data contents.

[0029] The first object of the present invention is also achieved by amethod including the steps of:

[0030] receiving the digital data contents and the digital watermarkdata;

[0031] dividing the digital data contents into block data;

[0032] obtaining a frequency coefficient of the block data;

[0033] obtaining an amount of transformation of the frequencycoefficient from the digital watermark data by using a quantizationwidth corresponding to the frequency coefficient, the quantization widthbeing obtained beforehand according to a manipulation method of thedigital data contents;

[0034] embedding the digital watermark data in said digital datacontents by transforming the frequency coefficient by the amount; and

[0035] generating watermarked digital data contents.

[0036] According to the above-mentioned inventions, the amount oftransformation of frequency coefficients is changed and/or the amount oftransformation is increased or decreased according to the complexity ofthe digital data contents. Therefore, the quality of the watermarkeddigital data contents can be improved and the durability of digitalwatermark data against a manipulation of the watermarked digital datacontents can be improved.

[0037] The second object of the present invention is achieved by amethod for reading digital watermark data embedded in digital datacontents, the method including the steps of:

[0038] receiving the digital data contents;

[0039] reading a bit sequence from the digital data contents;

[0040] calculating a probability of reading a bit ‘1’ or a bit ‘0’ inthe bit sequence by using a test method on the basis of binarydistribution;

[0041] determining the presence or absence of digital watermark dataaccording to the probability; and

[0042] reconstituting and generating the digital watermark data from thebit sequence.

[0043] According to the above-mentioned invention, probabilities of thefollowing cases can be evaluated quantitatively. The cases are thatdigital data contents which do not contain digital watermark data arewrongly judged as containing digital watermark data, and incorrectdigital watermark data is read from watermarked digital data contents.In addition, the probability can be suppressed within a constant value.

[0044] The third object of the present invention is achieved by a methodfor reading digital watermark data from digital data contents in whicheach bit of digital watermark data is embedded a plurality of times, themethod including the steps of:

[0045] receiving digital data contents;

[0046] reading a digital watermark sequence from the digital datacontents;

[0047] performing soft decision in code theory by assigning weights tothe digital watermark sequence with a weighting function;

[0048] reconstituting the digital watermark data from the digitalwatermark sequence.

[0049] According to the above-mentioned invention, the digital watermarkdata sequence is separated from the noise so that error bits which areincluded in the digital watermark data sequence can be reduced, therebythe digital watermark data reading success rate being improved incomparison with the conventional method. In addition, since weights areassigned to the digital watermark data sequence, the present inventionis especially effective when the repeating number of watermark embeddingis small.

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Other objects, features and advantages of the present inventionwill become more apparent from the following detailed description whenread in conjunction with the accompanying drawings, in which:

[0051]FIG. 1 is a block diagram of a digital watermarking system of thepresent invention;

[0052]FIG. 2 is a general flowchart showing a digital watermarkembedding process according to a conventional technique;

[0053]FIG. 3 is a detailed flowchart showing a principal part of thedigital watermark embedding process according to the conventionaltechnique;

[0054]FIG. 4 is a conceptual diagram of the digital watermark embeddingprocess according to the conventional technique;

[0055]FIG. 5 is a general flowchart showing a digital watermark readingprocess according to the conventional technique;

[0056]FIG. 6 is a detailed flowchart showing a principal part of thedigital watermark reading process according to the conventionaltechnique;

[0057]FIG. 7 is a block diagram showing receiving data and generatingdata of a digital watermark embedding apparatus of the presentinvention;

[0058]FIG. 8 is a block diagram showing receiving data and generatingdata of a digital watermark reading apparatus of the present invention;

[0059]FIG. 9 is a general flowchart showing a digital watermarkembedding process according to a first embodiment of the presentinvention;

[0060]FIG. 10 is a detailed flowchart showing a principal part of thedigital watermark embedding process according to the first embodiment ofthe present invention;

[0061]FIGS. 11A and 11B are conceptual diagrams of the digitalwatermark-embedding process according to the first embodiment of thepresent invention;

[0062]FIG. 12 is a flowchart of a process for calculating a datacomplexity according to a second embodiment of the present invention;

[0063]FIG. 13 is a flowchart showing a process for obtaining a watermarkweight ratio data according to the present invention;

[0064]FIG. 14 is a detailed flowchart showing a principal part of thedigital watermark embedding process according to a third embodiment ofthe present invention;

[0065]FIG. 15 is a detailed flowchart showing a principal part of thedigital watermark reading process according to a fourth embodiment ofthe present invention;

[0066]FIG. 16 is a flowchart showing a process of calculating awatermark strength matrix according to a fifth embodiment of the presentinvention;

[0067]FIG. 17 is a block diagram of a computer;

[0068]FIG. 18 is a block diagram of an integrated circuit;

[0069]FIG. 19 is a block diagram of a digital watermarking system of thepresent invention;

[0070]FIG. 20 is a block diagram of a digital watermark readingapparatus shown in FIG. 19;

[0071]FIG. 21 is a diagram for explaining judgment on digital watermarkdata;

[0072]FIG. 22 is a conceptual diagram of reconstituting digitalwatermark data;

[0073]FIG. 23 is a flowchart of a digital watermark reading processaccording to a seventh embodiment of the present invention;

[0074]FIG. 24 is a block diagram of a digital watermarking systemaccording to an eighth embodiment of the present invention;

[0075]FIG. 25 is a flowchart of a digital watermark reading processaccording to a tenth embodiment of the present invention;

[0076]FIG. 26 is a flowchart of a digital watermark reading processaccording to a tenth embodiment of the present invention when readingdigital watermark data sequence which is embedded after being modulatedby a pseudo-random sequence;

[0077]FIG. 27 is a diagram showing the result of reading a digitalwatermark data sequence without modulation;

[0078]FIG. 28 is a diagram showing the result of reading a modulateddigital watermark data sequence;

[0079]FIG. 29 is a diagram showing a digital watermark reading processaccording to a conventional technique;

[0080]FIG. 30 is a graph showing how MPEG-1 coding changes ‘1’ data bit,specifically the graph shows occurrence frequency with respect to changeamount of a DCT coefficient value by 1.5-Mbps MPEG-1 coding;

[0081]FIG. 31 is a flowchart showing a principle of a thirteenthembodiment of the present invention corresponding to a third object;

[0082]FIG. 32 is a block diagram of a digital watermark readingapparatus according to the thirteenth embodiment of the presentinvention;

[0083]FIG. 33 is a general flowchart showing a digital watermark readingprocess according to the thirteenth embodiment of the present invention;

[0084]FIG. 34 is a diagram showing the result of comparison of a digitalwatermark data reading success rate between a conventional readingmethod and the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0085] Before explaining embodiments of the present invention,definition of some words will be given. “Digital watermark datasequence” represents a data sequence read from the digital data contentsbefore being reconstituted. “Digital watermark data” representssignificant data for system operation, which data needs to be embeddedin the digital data contents, or, data obtained by reconstituting thedigital watermark sequence. “Reliability α of digital watermark” is anindex representing validity of read digital watermark data. That is, itrepresents a probability that the read digital watermark data matcheswith the actual embedded digital watermark data. Conversely, aprobability of reading digital watermark data from an image withoutdigital watermark data or reading erroneous digital watermark data canbe represented as 2(1−α). Similarly, “embedded sequence” represents datato be actually embedded. The embedded sequence includes sequence ofembedded data which is modulated, extended or repeated. In addition,“read” may be replaced with “extract” in some cases.

[0086]FIG. 1 shows a digital watermarking system of the presentinvention. In the system shown in FIG. 1, digital watermark data 101 isembedded in digital data contents 103 by a digital watermark embeddingapparatus 102, then, converted into watermarked digital data contents104.

[0087] The watermarked digital data contents 104 are degraded towatermarked digital data contents 105 by compression or image processingwhile the watermarked digital data contents 104 are distributed bywireless or wire communication or by a packaged medium.

[0088] A digital watermark reading apparatus 106 reads a watermarksequence from the degraded watermarked digital data contents 105, andreconstitutes digital watermark data 107.

[0089] In the following, a digital watermark embedding method and adigital watermark reading method by using quantization will bedescribed, since embodiments of the present invention are based on themethods. After the description of the methods, the embodiments of thepresent invention will be described.

[0090] According to the digital watermarking technique based onquantization, digital watermark data is embedded by quantizing all or apart of data which is transformed (for example, by an orthogonaltransform) from original digital data contents, or not-yet-transformeddata. As for digital watermark data reading, data in the contents inwhich digital watermark data is embedded is quantized by the same valueas a value used for embedding digital watermark data, and, then digitalwatermark data is determined from the quantized data value.

[0091] In the following, a general outline of the methods will bedescribed. The Japanese patent application No.9-57516, “Image processingmethod and the apparatus”, and the Japanese patent applicationNo.9-164466, “Information embedding method, data reading method and theapparatus”, and the like can be referred to for obtaining detailedinformation of the digital watermarking technique based on quantization.

[0092] First, digital watermark embedding method based on quantizationwill be described. A process of the method is carried out by the digitalwatermark embedding apparatus 102 shown in FIG. 1. FIG. 2 is a flowchartshowing the process.

[0093] The digital watermark embedding apparatus 102 obtains block data109 by dividing digital data contents 103 into a plurality of blocks (mblocks in this example) in step 100. Then, a frequency coefficientmatrix 115 (an orthogonal transform coefficient matrix) is generated byperforming an orthogonal transform on the block data 108 in step 110.

[0094] A pseudo-random sequence 125 is generated from input key data 12in step 120. Then, a coefficient (for each block) from the coefficientmatrix 115 is selected one by one using the pseudo-random sequence 125so as to generate a frequency coefficient sequence 135 to be watermarkedin step 130. Each bit of the digital watermark data 101 are diffused byrepeating number (t) of embedding so that a digital watermark sequence145 is generated in step 140. The digital watermark sequence 145 isembedded into the frequency coefficient sequence 135 such that awatermarked frequency coefficient sequence 155 is generated in step 150.

[0095] After that, the frequency coefficient sequence 135 in thefrequency coefficient matrix 115 is replaced by the watermarkedfrequency coefficient sequence 155 to generate a watermarked frequencycoefficient matrix 165 in step 160. Then, the watermarked frequencycoefficient matrix 165 is inverse-orthogonal-transformed to form awatermarked block data 175 in step 170. After that, the block data partof the input digital data contents 103 is replaced by the watermarkedblock data 175 in step 180. As a result, a watermarked digital datacontents is output.

[0096] In the above description, data in which digital watermark data isembedded is assumed to be the coefficient of the frequency coefficientmatrix. However, the data can be a pixel. In addition, when selecting acoefficient value from a block image, the number of the selectedcoefficient is not limited to one, that is, it can be more than one orzero. The present invention does not depend on the matter.

[0097] In the process of diffusing the digital watermark data shown inFIG. 2, for example, a process represented by s[j][k]=w[j] is carriedout for all j and k, then, the digital watermark data (w[0],w[1], . . .,w[n−1]) is transformed to the digital watermark data sequences[0][0],s[0][1], . . . ,s[0][t−1],s[1][0],s[1][1], . . .,s[1][t−1],s[n−1][0],s[n−1][1], . . . ,s[n−1][t−1].

[0098] In the watermark embedding process, quantization widths offrequency coefficients q[0],q[1], . . . ,q[m−1] are used.

[0099] In the following, the watermark embedding process (step 150) willbe described in detail with reference to a flowchart shown in FIG. 3.

[0100] Let the repeating number t of each bit of the digital watermarkdata be ${t = \left\lfloor \frac{m}{n} \right\rfloor},$

[0101] the frequency sequence be w[j],s[j][k]ε{0,1} {0≦j<n,0≦k<t}.

[0102] The watermark embedding process to the frequency sequence {f[i]}is carried out as follows.

[0103] 1. Following steps are carried out for all i$\left( {0 \leq i < {\left\lfloor \frac{m}{n} \right\rfloor \cdot n}} \right).$

[0104] 2. A watermarked frequency coefficient f′[i] is obtained from thefrequency coefficient f[i] according to following steps.${{\left. i \right)\quad {If}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad {mod}\quad 2\quad {is}\quad {equal}\quad {to}\quad {{s\lbrack X\rbrack}\lbrack Y\rbrack}},\left. {f^{\prime}\lbrack i\rbrack}\leftarrow\quad {\left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad \times {q.{ii}}\text{)}\quad {If}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad {mod}{\quad \quad}2\quad {is}\quad {different}\quad {from}\quad {{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad {and}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad {is}\quad {equal}\quad {to}\quad \left\lfloor \frac{f\lbrack i\rbrack}{q} \right\rfloor} \right.,\left. {f^{\prime}\lbrack i\rbrack}\leftarrow{\left( \quad {\left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad + 1} \right) \times {q.\quad {iii}}\text{)}\quad {If}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad {mod}\quad 2\quad {is}\quad {different}\quad {from}\quad {{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad {and}{\quad \quad}\left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad {is}\quad {different}\quad {from}\quad \left\lfloor \frac{f\lbrack i\rbrack}{q} \right\rfloor} \right.,\left. {f^{\prime}\lbrack i\rbrack}\leftarrow{\left( \quad {\left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad - 1} \right) \times {q.}} \right.}\quad$

[0105] Here, X=i/t and Y=i mod t. In addition, └x┘ represents a maximumnumber which does not exceed x and x mod y represents the remainder of xdivided by y.

[0106]FIG. 4 shows the concept of the conventional watermark embeddingprocess. As shown in the figure, digital watermark data is embedded bychanging a data value of watermarking area to a central value of thequantization width.

[0107] Next, the digital watermark reading method based on quantizationwill be described. The process is carried out in the digital watermarkreading apparatus 106. According to the digital watermark readingprocess, a digital watermark data sequence is read from watermarkedcontents, and, then digital watermark data is reconstituted bystatistically processing the digital watermark data sequence.

[0108]FIG. 5 is a flowchart showing the conventional digital watermarkreading process based on quantization.

[0109] The digital watermark reading apparatus 106 obtains watermarkedblock data 205 by dividing watermarked digital data contents 105 into aplurality of blocks (m blocks in this example) in step 200. Then, afrequency coefficient matrix 215 is generated by performing anorthogonal transform on the watermarked block data 205 in step 210.

[0110] A pseudo-random sequence 225 is generated from input key data 22in step 220. Then, a coefficient value (for each block) of the frequencycoefficient matrix 215 is selected one by one using the pseudo-randomsequence 225 so as to generate a watermarked frequency coefficientsequence 235 in step 230. Then, the watermark reading process isperformed on the watermarked frequency sequence 235 so that a digitalwatermark sequence 245 is read in step 240. Finally, the originalwatermark data 107 is output by performing statistical processing on thedigital watermark data sequence in step 250.

[0111] Next, the digital watermark reading process (step 240) will bedescribed in detail with reference to a flowchart in FIG. 6. The processfor reading the digital watermark sequence from the watermarkedfrequency coefficient sequence {f′[i]} is shown in the following.

[0112] 1. Following steps are carried out for all$i\left( {0 \leq i < {\left\lfloor \frac{m}{n} \right\rfloor \cdot n}} \right)$

[0113] by using a frequency coefficient quantization width q.

[0114] 2. The digital watermark sequence s[X][Y] is read from thefrequency coefficient f′[i]. That is,${{s\lbrack X\rbrack}\lbrack Y\rbrack} = {\left\lfloor {\frac{f^{\prime}\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad {mod}\quad 2.}$${Here},\quad {X = {{\left\lfloor \frac{i}{t} \right\rfloor \quad Y} = {i\quad {mod}\quad {t.}}}}$

[0115] When the digital watermark data is reconstituted from the digitalwatermark data sequence by performing statistical processing, a majoritydecision method such as ${W\lbrack j\rbrack} = \left\{ {\begin{matrix}1 & {{\sum\limits_{k = 0}^{t - 1}{{s\lbrack j\rbrack}\lbrack k\rbrack}} \geq \frac{t}{2}} \\0 & {{\sum\limits_{k = 0}^{t - 1}{{s\lbrack j\rbrack}\lbrack k\rbrack}} < \frac{t}{2}}\end{matrix}\quad \left( {0 \leqq j < n} \right)} \right.$

[0116] is used.

[0117] Next, the present invention corresponding to the first objectwill be described.

[0118]FIG. 7 is a block diagram showing input data and output data ofthe digital watermark embedding apparatus of the present invention. Thedigital watermark embedding apparatus 102 inputs digital data contents103 such as an image and a sound as main data, key data 12 and digitalwatermark data 101 as sub-data. The digital watermark embeddingapparatus 102 embeds digital watermark data 101 into the digital datacontents 103 and outputs watermarked digital data contents 104.

[0119]FIG. 8 is a block diagram showing input data and output data ofthe digital watermark reading apparatus of the present invention. Thedigital watermark reading apparatus 20 inputs the watermarked digitaldata contents 21 and the key data 22, and outputs digital watermark data23 embedded in the watermarked digital data contents 21. Here, the keydata 22 is the same as the key data 12.

[0120] In the following, embodiments of the present invention will bedescribed.

[0121] (First Embodiment)

[0122] A first embodiment of the present invention will be described.According to the first embodiment, digital data contents and digitalwatermark data is received and the digital data contents are dividedinto block data. Then, a frequency coefficient of the block data and thecomplexity is obtained. Next, an amount of transformation of thefrequency coefficient is obtained from the complexity and the digitalwatermark data by using a quantization width, and the digital watermarkdata is embedded by transforming the frequency coefficient by theamount. Then, watermarked digital data contents is generated.

[0123] The process of the first embodiment is a modified process of thedigital watermark embedding process shown in FIG. 2, in which themodified part is the main part for watermark embedding.

[0124]FIG. 9 is a flowchart of the whole process of the firstembodiment. In FIG. 9, a step 190 which calculates the complexity and awatermark embedding process for varying the transformation amountaccording to the complexity (steps 195, 150) are different from theconventional process shown in FIG. 2. Therefore, the different pointwill be mainly described in the following.

[0125] Block data 108 is input, and a complexity sequence 195 isgenerated by calculating a data complexity e[i](0≦e[i]≦1) for each blockdata in step 190. Then, the coefficient value of data to be watermarkedis transformed to a value within quantization width according to thedata complexity. In this embodiment, it is possible to use aconventional method for calculating the data complexity. For example, inthe case of an image, a process for obtaining local image complexity canbe used. In this case, it is necessary to normalize the range of thelocal complexity such that the range becomes from 0 to 1, if the rangeis from −α to +β.

[0126] Next, the watermark embedding process which is the heart of thesecond embodiment will be described in detail. FIG. 10 is a flowchartshowing the watermark embedding process (step 150 in FIG. 9) in detail.

[0127] The process for embedding digital watermark data into a frequencycoefficient sequence {f[i]} of the first embodiment is carried out asfollows.

[0128] 1. For all i$\left( {0 \leq i < {\left\lfloor \frac{m}{n} \right\rfloor \cdot n}} \right),$

[0129] the following process is carried out.

[0130] 2. A watermarked coefficient f′[i] is obtained from a coefficientf[i].${\left. i \right)\quad {If}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad {mod}\quad 2\quad {is}\quad {equal}\quad {to}\quad {{s\lbrack X\rbrack}\lbrack Y\rbrack}},\left. {f^{\prime}\lbrack i\rbrack}\leftarrow\quad {{f\lbrack i\rbrack} + {\left( {{\left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad \times q} - {f\lbrack i\rbrack}} \right) \times {e\lbrack i\rbrack}}} \right.$${{{ii}\text{)}\quad {If}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad {mod}{\quad \quad}2\quad {is}\quad {not}\quad {equal}\quad {to}\quad {{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad {and}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad {is}\quad {equal}\quad {to}\quad \left\lfloor \frac{f\lbrack i\rbrack}{q} \right\rfloor},\left. {f^{\prime}\lbrack i\rbrack}\leftarrow{\left( \quad {\left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad + \frac{{e\lbrack i\rbrack} + 1}{2}} \right) \times q} \right.}\quad$${{{iii}\text{)}\quad {If}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad {mod}\quad 2\quad {is}\quad {not}\quad {equal}\quad {to}\quad {{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad {and}{\quad \quad}\left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad {is}\quad {not}\quad {equal}\quad {to}\quad \left\lfloor \frac{f\lbrack i\rbrack}{q} \right\rfloor},\left. {f^{\prime}\lbrack i\rbrack}\leftarrow{\left( \quad {\left\lfloor {\frac{f\lbrack i\rbrack}{q} + \frac{1}{2}} \right\rfloor \quad - \frac{{e\lbrack i\rbrack} + 1}{2}} \right) \times {q.}} \right.}\quad$

[0131] Here, q represents the quantization width for digital watermarkdata embedding, X=i/j,Y=imodt, and └x┘ is the maximum integer which doesnot exceed x, and x mod y represents the remainder of x divided by y.

[0132]FIGS. 11A and 11B are conceptual diagrams showing the digitalwatermark embedding process of the first embodiment. As shown in FIG.11B, a data complexity e[i](0≦e[i]≦1) is calculated for each block data,then, the value of data in which digital watermark data is embedded istransformed to a value within the quantization width according to thedata complexity.

[0133] Generally, the quality of the watermarked digital data contentsis a trade-off for the strength of the digital watermark data. However,according to the present invention, both of the quality of thewatermarked digital data contents and the watermark durability can beimproved while keeping the quality and the durability in balance. Thatis, digital watermark data is embedded according to the local datacomplexity. Specifically, digital watermark data is embedded with agreater strength in a complex part, and is embedded with a weakerstrength in a non-complex part.

[0134] The watermarking technique has an embedding process and a readingprocess in a pair. However, even if the embedding process is modifiedfrom the conventional process according to the present invention, thereading process does not need to be changed from the conventionalreading process for reading the digital watermark data which is embeddedby the method of the present invention.

[0135] (Second Embodiment)

[0136] In the following, a second embodiment of the present inventionwill be described. The second embodiment relates to the process forcalculating the data complexity (step 190 in FIG. 9).

[0137] According to the second embodiment, the block data is transformedby applying Wavelet transform. Then, high frequency coefficient data ofthe wavelet transformed data is filtered by using a threshold value, andthe complexity of the block data is calculated from the number of thedata values which exceed the threshold.

[0138]FIG. 12 is a flowchart of the process for calculating the datacomplexity according to the second embodiment. Here, let the dimensionof a block data B[i] be N, and let the size of the block data be M₀×M₁ .. . ×M_(N−1). A following process is performed on each elementh_(v0,v1, . . . ,vN−1)(0<v_(u)<M_(u)/2, 0<u<N) of the high frequencycoefficient matrix H₀×H₁ . . . ×H_(N−1) of N dimensional wavelettransformed block data.

[0139] 1. count←0

[0140] b 2. For all (v₀,v₁, . . . ,v_(N−1)), a step 3 is carried out (Ndimensional loop).

[0141] 3. For a threshold Δ≧0 which is set beforehand, If |hv₀,v₁, . . .,v_(N−1)|≧Δ, count←count+1. Here, |X| represents the absolute value ofx.

[0142] 4. For a threshold Γ≧0 which is set beforehand, If count≧Γ,e[i]←1.0. If not,$\left. {e\lbrack i\rbrack}\leftarrow{\frac{count}{\Gamma}.} \right.$

[0143] In the process for calculating the data complexity, for example,if it is assumed that N=2 (an image), the basis of the wavelet transformis the Haar basis, M₀=16 and M₁=16, an experiment shows that values ofΔ=4 and Γ=16 are good for the balance for embedding digital watermarkdata without being notified by a human.

[0144] According to the second embodiment, the above-mentioned functioncan be realized by setting the two thresholds Δ and Γ according to thecharacteristics of the watermarking technique such as the kind of datato be watermarked, a unit (the size of the block data), the kind oforthogonal transform to be used. By applying the above-mentionedfunction to the watermarking technique, it becomes possible to embeddigital watermark data more appropriately according to characteristicsof individual digital data contents.

[0145] (Third Embodiment)

[0146] In the following, a fourth embodiment of the present inventionwill be described.

[0147] According to the third embodiment, in the digital watermarkembedding process, block data of digital data contents is obtained, anda transformation amount of frequency coefficient is calculated on thebasis of a transformation amount for each frequency band according to amanipulation method of the digital data contents. Then, block data ofthe watermarked digital data contents is generated.

[0148] Let the dimension of a block data B[i] be N and the size be M₀×M₁. . . ×M_(N−1). Here, a sequence which represents the ratio oftransformation width for the frequency band of each frequencycoefficient needs to be obtained beforehand by using adequate digitaldata contents before operating a digital watermarking system. Thecalculation method for obtaining q[i] will be described in detail in afifth embodiment later.

[0149]FIG. 13 is a flowchart for obtaining the ratio of the quantizationwith for each frequency band. First, digital data contents 1000 isinput, and block data 1015 is obtained by dividing the input digitaldata contents into blocks in step 1010. The block data 1015 istransformed to first frequency coefficient matrices by applying theorthogonal transform in step 1020. Next, digital data contents 1035 isgenerated by performing a manipulation such as non-reversiblecompression on the digital data contents 1000 in step 1030. Then, blockdata 1045 is generated by dividing the digital data contents 1035 intoblocks in step 1040. Second frequency matrices 1055 is generated byapplying the orthogonal transform to the block data 1015 in step 1055.Then, the variance of the distribution of the difference between eachelement of the frequency coefficients matrices 1025 and each element ofthe frequency coefficients matrices 1055 is obtained in step 1060.Finally, watermark weight ratio data d v₀,v₁, . . . ,v_(N−1) 1070 whichrepresents the ratio of transformation for each frequency coefficient isobtained. The watermark weight ratio data obtained in this way isstored, and it is used in a watermark embedding process and a watermarkreading process as necessary. The quantization width is obtained as dv₀,v₁, . . . ,v_(N−1)×Power which will be described next.

[0150]FIG. 14 is a flowchart showing the watermark embedding processwhich is the heart of the third embodiment of the present invention.Here, the flow of the whole process is the same as that shown in FIG. 2or FIG. 9.

[0151] Let the watermark weight ratio sequence be {dv₀,v₁, . . .,v_(N−1)} (0≦v_(u)<M_(u),0≦u<N), and let the watermark strength be Power(the watermark strength represents durability of digital watermark dataagainst manipulations of watermarked digital data contents.)

[0152] The watermark embedding process of the embodiment is carried outas follows.

[0153] 1. For all i$\left( {0 \leq i < {\left\lfloor \frac{m}{n} \right\rfloor \cdot n}} \right),$

[0154] a following process is carried out.

[0155] 2. A quantization width q[i] used when embedding digitalwatermark data into the frequency coefficient f[i] is obtained byq[i]←dv₀,v₁, . . . ,v_(N−1)×Power by using an element dv₀,v₁, . . .,v_(N−1) of the watermark weight ratio sequence which corresponds to theband of the frequency coefficient f[i] (f[i] is a (v₀,v₁, . . .,v_(N−1)) th component of the frequency coefficient matrices).

[0156] 3. The watermarked frequency coefficient f′[i] is obtained fromthe frequency coefficient f[i] in the following way.${\left. i \right)\quad {If}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor \quad {mod}\quad 2\quad {is}\quad {equal}\quad {to}\quad {{s\lbrack X\rbrack}\lbrack Y\rbrack}},\left. {f^{\prime}\lbrack i\rbrack}\leftarrow{\left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor \quad \times {{q\lbrack i\rbrack}.{ii}}\text{)}\quad {If}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor \quad {mod}{\quad \quad}2\quad {is}\quad {not}\quad {equal}\quad {to}\quad {{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad {and}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor \quad {is}\quad {equal}\quad {to}\quad \left\lfloor \frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} \right\rfloor} \right.,\left. {f^{\prime}\lbrack i\rbrack}\leftarrow{\left( \quad {\left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor \quad + 1} \right) \times {q\quad\lbrack i\rbrack}} \right.$${{{iii}\text{)}\quad {If}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor \quad {mod}\quad 2\quad {is}\quad {not}\quad {equal}\quad {to}\quad {{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad {and}{\quad \quad}\left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor \quad {is}\quad {not}\quad {equal}\quad {to}\quad \left\lfloor \frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} \right\rfloor},\left. {f^{\prime}\lbrack i\rbrack}\leftarrow{\left( \quad {\left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor \quad - 1} \right) \times {{q\lbrack i\rbrack}.}} \right.}\quad$

[0157] Here, X=i/t, Y=i mod t, and └x┘ is the maximum integer which doesnot exceed x, and x mod y represents the remainder of x divided by y.

[0158] (Fourth Embodiment)

[0159] In the following, a fourth embodiment of the present inventionwill be described.

[0160] The fourth embodiment is a watermark reading processcorresponding to the watermark embedding process of the thirdembodiment. According to the fourth embodiment, block data ofwatermarked digital data contents is obtained, and digital watermarkdata is read from frequency coefficients on the basis of transformationamount for each frequency band according to a manipulation method of thedigital data contents.

[0161]FIG. 15 is a flowchart showing the watermark reading process ofthe fourth embodiment of the present invention. Here, as in the case ofthe third embodiment, let the watermark weight ratio sequence be{dv₀,v₁, . . . ,v_(N−1)} (0≧v_(u)<M_(u),0≦u<N), and let the watermarkstrength be Power (the watermark strength represents durability ofdigital watermark data against manipulations such as non-reversiblecompression to watermarked digital data contents.)

[0162] The process for reading the digital watermark data sequence fromthe watermarked frequency coefficient according to the fourth embodimentis carried out as follows.

[0163] 1. For all i$\left( {0 \leq i < {\left\lfloor \frac{m}{n} \right\rfloor \cdot n}} \right),$

[0164] a following process is carried out.

[0165] 2. A quantization width q[i] used when reading digital watermarkdata from the frequency coefficient f′[i] is obtained by q[i]←dv₀,v₁, .. . ,v_(N−1)×Power by using an element dv₀,v₁, . . . ,v_(N−1) of thewatermark weight ratio sequence which corresponds to the band offrequency coefficient f[i] (f[i] is a (v₀,v₁, . . . ,v_(N−1)) thcomponent of the frequency coefficient matrices).

[0166] 3. The digital watermark data sequence s[X][Y] is read from thewatermarked frequency coefficient f′[i] in the following way.$\left. {{s\lbrack X\rbrack}\lbrack Y\rbrack}\leftarrow{\left\lfloor {\frac{f^{\prime}\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor \quad {mod}\quad 2} \right.$${Here},\quad {X = {{\left\lfloor \frac{i}{t} \right\rfloor \quad {and}\quad Y} = {i\quad {mod}\quad {t.}}}}$

[0167] According to the above-mentioned third and fourth embodiment, thewatermark embedding strength can be changed according to the frequencyband. Specifically, the watermark embedding and reading methodapplicable for a manipulation method becomes possible. In the method,according to the amount of change of digital data contents from originaldata for each frequency band due to manipulation such as non-reversiblecompression, the watermark strength is raised to a band when the amountis large, and the watermark strength is reduced when the amount issmall. Accordingly, both of the quality of watermarked digital datacontents and the durability of digital watermark data can be improved ata time.

[0168] (Fifth Embodiment)

[0169] In the following, a fifth embodiment of the present inventionwill be described. According to the fifth embodiment, a number ofdigital data contents (images, sounds and the like) are prepared andcalculation of a watermark strength matrix is carried out for eachfrequency band.

[0170] A processing flow of the fifth embodiment is the same as thatshown in FIG. 13 basically. Here, the orthogonal transform process shownin FIG. 13 is the same as an orthogonal transform process used fordigital watermarking process. For example, if the orthogonal transformused for digital watermarking is discrete cosine transformation (DCT)for a 16×16 size, the DCT is used, and, if the transformation used fordigital watermarking is fast Fourier transform (FFT) for an 128×128size, the FFT is used.

[0171]FIG. 16 is a flowchart showing the process of calculating thewatermark strength matrix for each frequency band according to the fifthembodiment.

[0172] Here, let the frequency coefficient matrices be N, the size beM₀×M₁ . . . ×M_(N−1), and each of the components bex0_(v0,v1, . . . ,vN−1), xt_(v0,v1, . . . ,vN−1)(0≦v_(u)<M_(u), 0≦u<N).The process shown in FIG. 16 is as follows.

[0173] 1. For all i (0≦i<m), the following steps 2 and 3 are performed.

[0174] 2. For all (v₀, v₁, . . . , v_(N−1))=(0, 0, . . . , 0)˜(M₀, M₁, .. . ,M_(N−1)), the process of the following step 3 is performed.3.  y_(v₀, v₁,  …  ,  v_(N − 1))^((i)) ← xo_(v₀, v₁,  …  , v_(N − 1)) − xt_(v₀, v₁,  …  , v_(N − 1))

[0175] 4. For all (v₀, v₁, . . . , v_(N−1))=(0, 0, . . . , 0)˜(M₀, M₁, .. . ,M_(N−1)), the following steps 5 and 6 are performed.$\begin{matrix}\left. {5.\quad A_{v_{0},v_{1},\quad \ldots \quad,v_{N - 1}}}\leftarrow\frac{\sum\limits_{i = 0}^{m - 1}y_{v_{0},v_{1},\quad \ldots \quad,v_{N - 1}}^{i}}{m} \right. \\\left. {6.\quad d_{v_{0},v_{1},\quad \ldots \quad,v_{N - 1}}}\leftarrow\sqrt{\frac{\sum\limits_{i = 0}^{m - 1}\left( {y_{v_{0},v_{1},\quad \ldots \quad,v_{N - 1}}^{i} - A_{v_{0},v_{1},\quad \ldots \quad,v_{N - 1}}} \right)^{2}}{m}} \right.\end{matrix}$

[0176] According to the fifth embodiment, it becomes possible to set thewatermark strength to a level that is suitable for each frequency bandaccording to a manipulation method for digital data contents such asnon-reversible compression. For example, if the watermark strength isPower and the distribution of the amount of change of each coefficientvalue of the frequency coefficients after a manipulation can beapproximated by a Laplacian distribution, when digital watermark data isread from digital data contents on which an assumed manipulation isperformed, the rate of bit reversal for the extracted digital watermarkdata can be made constant $^{- \frac{Power}{\sqrt{2}}}$

[0177] regardless of the frequency band (e is the natural logarithm). Itis the advantage of the present invention to be able to predict the rateof bit reversal with the constant formula. In addition, according to theembodiment of the present invention, one of the problem of theconventional method that durability of embedded digital watermark datais varied according to the position of the frequency coefficient issolved. That is, the durability of the embedded digital watermark datais constant regardless of the position of the frequency coefficient(which is obvious from the above formula). The embodiment can be appliednot only to the watermarking method based on quantization but also to awatermarking method based on the spread spectrum technique.

[0178] (Sixth Embodiment)

[0179] In the following, a sixth embodiment of the present inventionwill be described. According to the sixth embodiment, the digitalwatermark embedding process is carried out by utilizing the firstembodiment and the third embodiment in combination. The watermarkembedding process of the sixth embodiment will be described as amodification of the step 150 shown in FIG. 9.

[0180] According to the sixth embodiment, the process for embeddingdigital watermark data in a frequency coefficient sequence {f[i]} is asfollows.

[0181] 1. For all i$\left( {0 \leq i < {\left\lfloor \frac{m}{n} \right\rfloor \cdot n}} \right),$

[0182] the following is performed.

[0183] 2. A quantization width q[i] used when embedding digitalwatermark data into the frequency coefficient f[i] is obtained byq[i]←dv₀,v₁, . . . ,v_(N−1)×Power by using an element dv₀,v₁, . . .,v_(N−1) of the watermark weight ratio sequence which corresponds to theband of the frequency coefficient f[i].

[0184] 3. The watermarked coefficient f′[i] is obtained from thefrequency coefficient f[i] in the following way.${i\text{)}\quad {If}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor \quad {mod}\quad 2\quad {is}\quad {equal}\quad {to}\quad {{s\lbrack X\rbrack}\lbrack Y\rbrack}},\left. {f^{\prime}\lbrack i\rbrack}\leftarrow{{f\lbrack i\rbrack} + {\left( {{\left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor \times {q\lbrack i\rbrack}} - {f\lbrack i\rbrack}} \right) \times {{e\lbrack i\rbrack}.{ii}}\text{)}\quad {If}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor \quad {mod}\quad 2\quad {is}\quad {not}\quad {equal}\quad {to}\quad {{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad {and}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor \quad {is}\quad {equal}\quad {to}\quad \left\lfloor \frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} \right\rfloor}} \right.,\left. {f^{\prime}\lbrack i\rbrack}\leftarrow{\left( {\left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor + \frac{{e\lbrack i\rbrack} + 1}{2}} \right) \times {{q\lbrack i\rbrack}.{iii}}\text{)}\quad {If}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor \quad {mod}\quad 2\quad {is}\quad {not}\quad {equal}\quad {to}\quad {{s\lbrack X\rbrack}\lbrack Y\rbrack}\quad {and}\quad \left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor \quad {is}\quad {not}\quad {equal}\quad {to}\quad {\left\lfloor \frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} \right\rfloor.{f^{\prime}\lbrack i\rbrack}}}\leftarrow{\left( {\left\lfloor {\frac{f\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor - \frac{{e\lbrack i\rbrack} + 1}{2}} \right) \times {{q\lbrack i\rbrack}.}} \right.$

[0185] Here, X=i/t, Y=i mod t, and └x┘ is the maximum integer which doesnot exceed x, and x mod y represents the remainder of x divided by y.

[0186] According to the sixth embodiment, both of the quality of thewatermarked digital data contents and the durability of digitalwatermark data can be further improved as compared with the firstembodiment and the third embodiment applied separately. The watermarkreading method shown in the fourth embodiment can be used as-is for awatermark reading method in the sixth embodiment.

[0187] The above-mentioned processes performed by the digital watermarkreading apparatus and the digital watermark embedding apparatusaccording to the present invention can be constructed by a program whichcan be stored in a computer readable medium such as a disk unit, afloppy disk, CD-ROM and the like. Then, by installing the program into acomputer from the medium, the present invention can be easily realized.FIG. 17 is a diagram showing the configuration example of the computer.As shown in the figure, the computer includes a CPU300, a memory 301, anexternal storage unit 302, a display 303, a keyboard 304 and acommunication processing unit 305. The digital watermarking process ofthe present invention is carried out by running the program stored inthe memory 301 on the CPU 300.

[0188] In addition, the digital watermark reading apparatus and thedigital watermark embedding apparatus can be realized also by anintegrated circuit shown in FIG. 18. The integrated circuit includes amemory part 401, a micro processor part 402, an interface part 403managing an interface to an outside part. Since, the configuration inFIG. 18 shows principal parts, the integrated circuit may includes otherparts. The program stored in the memory part 401 is carried out by amicro processor part 402. The integrated circuit can take various otherconfigurations. The integrated circuit can be incorporated to variousapparatuses such as a camera so that the apparatuses can perform thedigital watermarking process of the present invention.

[0189] As mentioned above, according to the present invention, the rateof the amount of change of frequency coefficients is changed, and/or,the amount of change of rate is increased or decreased according to thecomplexity of the digital data contents. Therefore, the quality of thewatermarked digital data contents can be improved and the durability ofdigital watermark data against a manipulation of the watermarked digitaldata contents can be improved.

[0190] Next, embodiments of the present invention corresponding to thesecond objectives will be described.

[0191] (Seventh Embodiment)

[0192] In the following, the seventh embodiment of the present inventionwill be described with reference to figures.

[0193]FIG. 19 is a block diagram of a digital watermarking system towhich the present invention relates. FIG. 19 shows a similarconfiguration to that shown in FIG. 1. The difference is that FIG. 19shows a digital watermark data reconstitution apparatus 108 which is anessential part of the present invention. The digital watermark datareconstitution apparatus 108 is provided in the watermark embeddingapparatus 106. In the system, a digital watermark data sequence is readfrom the watermarked digital data contents 105 by using the watermarkreading apparatus 106. Then, the digital watermark data sequence isprocessed in the digital watermark data reconstitution apparatus 108 sothat the read digital watermark data 107 is obtained.

[0194] In the following, the process for reconstituting the digitalwatermark data is described in detail.

[0195]FIG. 20 is a block diagram of the watermark reading apparatus 106.The digital watermark data reconstitution apparatus 108 provided in thewatermark reading apparatus 106 obtains the probability q that bit 1 isread when any 1 bit watermark sequence is read from a whole watermarkarea beforehand by using the watermark reading apparatus 106.

[0196] Specifically, assuming a 1 bit watermark sequence reading part501, the part 501 reads the watermark sequence 1 bit by 1 bit from allelements of the whole watermark area (a broken line L1), and calculatesthe ratio of the number of bit 1 to the number of all trials.

[0197] In the embodiment, the reading probability of bit 1 and thenumber of bit 1 are obtained. However, it is possible that the readingprobability of bit 0 and the number of bit 0 are obtained. Basically,there is no difference between the former and the latter. The differenceis only on implementation.

[0198] Accordingly, the probabilities of detecting bit 0 and 1 whenreading 1 bit at random in the watermark area by using the digitalwatermarking algorithm is calculated to be 1−q and q respectively.

[0199] The n bit watermark sequence reading part 502 reads the digitalwatermark data sequence from the watermarked digital data contents forthe number of total times of embedding digital watermark data.

[0200] Here, digital watermark data is defined as b₀, b₁, . . . ,b_(m−1), b_(i) ε{0, 1}, i<m (m bit length), the repeating number ofembedding ith bit of the digital watermark data in the digital datacontents is defined as n_(i), the read watermark sequence is defined as$b_{0,0}^{\prime},b_{0,1}^{,\prime},{\ldots \quad b_{0,{{n0} - 1}}^{\prime}},b_{1,0}^{\prime},b_{1,1}^{\prime},{\ldots \quad b_{1,{{n1} - 1}}^{\prime}},\ldots,\quad b_{{m - 1},0}^{\prime},b_{{m - 1},1}^{\prime},{{\ldots \quad b_{{m - 1},{{nm} - 1 - 1}}^{\prime}\quad b_{i,j}} \in {\left\{ {0,1} \right\} \quad {\left( {\sum\limits_{r = 0}^{m - 1}{n_{r}\quad {bit}\quad {length}}} \right).}}}$

[0201] length).

[0202] The data reconstitution apparatus 108 receives a subsequence ofthe digital watermark data sequence one after another from a subsequencecorresponding to 0th digital watermark data to a subsequencecorresponding to (m−1)th digital watermark data (a solid line L2).

[0203] Next, the method for reconstituting ith bit of the digitalwatermark data will be described concretely.

[0204] When n_(i) bits of digital watermark data sequence is read atrandom from the watermark area, the probability P(x=k) of k ‘1’ bitsappearing in the n_(i) bit sequence is represented by the binarydistribution density function

P(x=k)=n _(i) C _(k) q ^(k)·(1−q)^(ni−k)  (1)

[0205] and the distribution function of that, F(x), is $\begin{matrix}{{F(x)} = {\sum\limits_{k = 0}^{x}{n_{i}C_{k}{q^{k} \cdot \left( {1 - q} \right)^{{ni} - k}}{\left( {0 \leqq x \leqq n_{i}} \right).}}}} & (2)\end{matrix}$

[0206] Here, n_(i)C_(k) is the number of combinations when selecting kout of n_(i).

[0207] Setting a reliability threshold value α (½<α≦1) of the digitalwatermark data, the number of bit 1 included in a subsequence b′_(i,0),b′_(i,1), . . . b′_(i,ni−1) corresponding to ith digital watermark datais calculated by$k_{i} = {\sum\limits_{r = 0}^{{ni} - 1}{b_{i,r}^{\prime}.}}$

[0208] Then, digital watermark data is determined in the following wayby using the formula (2): $\begin{matrix}{b_{i} = \left\lbrack \begin{matrix}0 & {when} & {0 \leqq {F\left( k_{i} \right)} \leqq {1 - \alpha}} \\1 & {when} & {\alpha \leqq {F\left( k_{i} \right)} \leqq 1} \\\begin{matrix}{{unknown}\quad {or}} \\{{not}\quad {present}}\end{matrix} & {when} & {{1 - \alpha} < {F\left( k_{i} \right)} < \alpha}\end{matrix} \right.} & (3)\end{matrix}$

[0209] Viewing from a different angle, when determining by the number ofbit 1 included in the watermark sequence n_(i), if the largest integerx₀ that satisfies 0≦F(x=x₀)≦1−α and the smallest integer x₁ thatsatisfies α≦F(x=x₁)≦1 are assumed to be threshold values, the digitalwatermark data is judged as shown in FIG. 21 such that if the number of1 in n_(i) is equal to or smaller than x₀, the digital watermark data is0, and that if the number of 1 is equal to or larger than x₁, thedigital watermark data is 1.

[0210] The horizontal axis of FIG. 21 represents the number of bit 1included in the watermark sequence, and the vertical axis representsfrequency of the corresponding number. As for unwatermarked digital datacontents, the frequency that bit 1 appears in a bit sequence read atrandom from the digital data contents becomes binary distribution. Thus,the peak of the frequency is at the half point of the number of bits. Onthe other hand, as for watermarked contents, in the subsequence n_(i) inwhich bit 0 is embedded as digital watermark data, the frequency of bit1 is 0 if there is no degradation and it is a small number which isequal to or smaller than x₀ even if there is degradation. In thesubsequence n_(i) in which bit 1 is embedded as digital watermark data,the frequency of bit 1 is n1 if there is no degradation and it is alarge number which is equal to or larger than x₁ even if there isdegradation. In this way, the distribution of the frequency of bit 1 orbit 0 in the watermarked sequence is leaning to one side from the centerof the binary distribution. The present invention uses the lean forreconstituting digital watermark data from the read watermark sequence.

[0211] Depending on a watermarking system, a following method can beused. That is, reconstituted digital watermark data is obtained by usingthe bias from the central value of the distribution P(x) of thewatermark sequence extracted from digital data contents 105. Next, theprobability of appearing the read watermark sequence is calculated bythe formula (2). Then, if the reconstituted digital watermark data is 1,F(k_(i)) can be added to watermark dada as the reliability, and, if thereconstituted digital watermark data is 0, 1−F(k_(i)) can be added. Thereliability F(k_(i)) and 1−F(k_(i)) of the digital watermark data isobtained from the bias of appearance probability of the digitalwatermark data in the binary distribution of appearance probability ofeach bit of 1 bit sequence extracted at random from digital datacontents.

[0212]FIG. 22 shows a concept in which the length of the digitalwatermark data is extended to m bits.

[0213] The digital watermark data reconstitution apparatus 108 outputsthe reconstituted digital watermark data b₀, b₁, . . . , b_(m−1) as readdigital watermark data 107.

[0214]FIG. 23 is a flowchart showing the above-mentioned process. Theprocess will be described in the following with reference to FIG. 23.

[0215] Watermarked digital data contents 105 and key data which isnecessary for reading digital watermark data is input, and a digitalwatermark data sequence is extracted with respect to each bit value instep 1. Then, a threshold value α of the reliability is set in step 2,and a probability q that bit 1 appears when 1 bit of digital watermarkdata is read at random from the whole watermark area is obtained in step3. Then, a binary distribution function F(x) which representsprobability that x bits of 1 are included in the bit sequence isobtained from the probability q and the repeating number n_(i) of eachbit of digital watermark data in step 4.

[0216] Then, 0 is assigned to i which distinguish a subsequence of thedigital watermark data sequence in step 5. Next, the number of bit 1 inthe subsequence is obtained as$k_{i} = {\sum\limits_{r = 0}^{{ni} - 1}b_{i,r}^{\prime}}$

[0217] and the appearance probability F(k_(i)) is obtained, then it isdetermined whether F(k_(i)) is equal to or less than 1−α in step 6. IfF(k_(i))≦1−α, the digital watermark data w′_(i) is reconstituted as 0 instep 7. Then, i is incremented by 1 in step 8, and the process goes backto step 6 if i<m in step 9. If F(k_(i))≦1−α is not true in step 6, it ischecked whether F(k_(i))≧α is true in step 10. If F(k_(i))≧α, thedigital watermark data w_(i) is reconstituted as 1 in step 11, and theprocess goes to step 8. If F(k_(i))≧α is not true in step 10, theprocess ends by determining as there is no watermark or the presence orabsence is unknown in step 12. If i is more than n_(i) in step 9, areconstituted watermark sequence {w′_(i)} is output. In the aboveprocess, the reading process in step 1 can be carried out between step 4and step 5. In step 6, it is checked whether 1−F(k_(i)) is more than α.

[0218] In the seventh embodiment, it is assumed that there is no bias inthe distribution represented by formula (1), that is, q≅½.

[0219] When the embedding number n_(i) of each bit of digital watermarkdata is adequate for obtaining a statistical characteristic, it becomesq≅½ generally. However, since the value of q depends on characteristicsof an watermarking algorithm and digital data contents, q may take avalue deviating largely from ½ in some rare cases. A method for solvingthis problem will be described in a eighth embodiment.

[0220] (Eighth Embodiment)

[0221] In the following, the eighth embodiment will be described. FIG.24 is a block diagram of a watermarking system of the ninth embodiment.

[0222] The watermark embedding apparatus 102 embeds digital watermarkdata 101 in digital data contents 103. At the time, when embedding eachbit value n_(i) times repeatedly, watermark sequence is modulated andembedded in the digital data contents 103. The modulation is carried outby a pseudo-random sequence generator (A) 601 which is provided in thewatermark embedding apparatus 102.

[0223] For example, when assuming the embedding sequence as b_(0,0),b_(0,1), . . . b_(0,n0−1), b_(1,0), b_(1,1), . . . b_(1,n1−1), . . .,b_(m−1,0), b_(m−1,1), . . . b_(m−1,nm−1 −1) b_(i,j) ε{0, 1}, and thepseudo-random sequence as r_(i,0), r_(i,1), . . . r_(i,ni−1) b_(i,j)ε{0, 1 }, the embedding sequence is modulated to

m_(i,0), m_(i,1), . . . m_(i,ni−1)

m _(i,j) =b _(i,j)(+)r _(i,j)

[0224] by the pseudo-random sequence. A(+)B represents XOR of A and B.

[0225] According to the above-mentioned process, the same pseudo-randomsequence is necessary for digital watermark data reading.

[0226] For example, if 1 bit watermark sequence is read by using anM-sequence as the pseudo-random sequence, it becomes q≅½. Therefore, thepresent invention can be applicable without depending on thewatermarking algorithm and digital data contents.

[0227] When digital watermark data reading, demodulation is carried outas b′_(i,j)=m_(i,j)(+)r_(i,j) by using a pseudo-random sequencegenerator (B) 602 which is provided in the watermark reading apparatus106.

[0228] Here, the pseudo-random sequence generator (A) 601 and thepseudo-random sequence generator (B) 602 needs to be implemented suchthat both of the generators generate the same pseudo-random sequence.

[0229] Watermark data is reconstituted with the method of the seventhembodiment from the watermark sequence b′_(0,0), b′_(0,1), . . .b′_(0,n0−1), b′_(1,0), b′_(1,1), . . . b′_(1,n1−1), . . . ,b′_(m−1,0),b′_(m−1,1), . . . b′_(m−1,nm−1 −1) b_(i,j) 68 {0, 1} obtained by thedemodulation.

[0230] Since it is considered that the appearance probability q of bit 1in the watermark sequence can be approximated by the binary distributionregardless of the presence or absence of modulation, there is noinfluence on the distribution of the density function (1) due to themodulation shown in this embodiment.

[0231] In addition, q=½ can be assumed in implementation, that is, noprocess is necessary for obtaining q. Therefore, the amount ofprocessing that is required for watermark reconstitution thus becomesthe same as that for majority decision processing. Thus, thereconstitution process becomes faster.

[0232] (Ninth Embodiment)

[0233] In the following, a ninth embodiment will be described. In theninth embodiment, an example will be described showing concrete valueson the basis of the seventh embodiment and the eighth embodiment. Inthis embodiment, it is assumed that digital watermark data is 1 bit, therepeating number n of embedding is 127 and the probability q that bit 1is read when reading 1 bit watermark sequence at random from the wholewatermark area is ½. If the threshold value α is 0.99999 (which means99.999%), x₀ in FIG. 21 is 36 and x₁ is 90. That is to say, according tothe present invention, under the above-mentioned condition, digitalwatermark data is judged as bit 0 if the number of ‘1’ appeared in thewatermark sequence (n bits) is equal to or less than 36, and it isjudged as bit 1 if the number of ‘1’ appeared in the watermark sequence(n bits) is equal to or more than 90, and it is judged that there is nowatermark data or the presence or absence is unknown in other cases. Ifit is judged that there is digital watermark data, the correctness ofmore than 99.999% can be ensured.

[0234] (Tenth Embodiment)

[0235] A tenth embodiment will be described in the following. Accordingto the embodiment shown in FIG. 23, as is understood from theabove-mentioned procedure, if even the reliability of only 1 bit is notobtained, that is, if F(k_(i)) or 1−F(k_(i)) is less than α, thereconstitution of the digital watermark data becomes impossible becauseit is judged that there is no digital watermark data or the presence orabsence is unknown. The tenth embodiment solves the problem. In thiscase, it is assumed that the repeating number of embedding each bit ofdigital watermark data is the same value n.

[0236] The method for reconstituting digital watermark data w₀, w₁, . .. , w_(m−1) from watermark sequence b′_(0,0), b′_(0,1), . . .b′_(0,n0−1), b′_(1,0), b′_(1,1), . . . b′_(1,n−1), . . . ,b′_(m,0),b′_(m,1), . . . b′_(m,n−1) which is read from digital data contents willbe described in the following with reference to FIG. 25.

[0237] The watermark sequence is read with respect to each bit valuefrom the digital data contents and key data necessary for digitalwatermark data reading in step 1.

[0238] The threshold value α (½<α≦1) of the reliability is set in step2. For example, if the reliability of read digital watermark data needsto be equal to or more than 99%, it is set as α=0.99.

[0239] The probability q of bit ‘1’ when 1 bit of the watermark sequenceis read at random from the whole watermark area of watermarked digitaldata contents is obtained beforehand in step 3. The appearanceprobabilities of bits ‘0’ and ‘1’ are calculated as 1−q and qrespectively.

[0240] The probability that x bits of ‘1’ are included in the watermarksequence of each bit data of digital watermark data are obtained as${F(x)} = {\sum\limits_{j = 0}^{x}{{{}_{}^{}{}_{}^{}}{q^{j} \cdot \left( {1 - q} \right)^{n - j}}}}$

[0241] by using the binary distribution function in step 4.

[0242] It is checked in step 5 that the probability that n bit digitalwatermark data sequence is digital watermark data exceeds the thresholdvalue α. Specifically, it is checked whether the following formula (4)is satisfied. $\begin{matrix}{{F\left( {\frac{\sum\limits_{i = 0}^{m - 1}{{{\sum\limits_{j = 0}^{n - 1}b_{i,j}^{\prime}} - \frac{n}{2}}}}{m} + \frac{n}{2}} \right)} \geq \alpha} & (4)\end{matrix}$

[0243] Here, |a| represents the absolute value of a.${\sum\limits_{j = 0}^{n - 1}b_{i,j}} - \frac{n}{2}$

[0244] represents the bias from the center of the binary distribution ofthe number of bit ‘1’ in the n bit watermark sequence.${\sum\limits_{i = 0}^{m - 1}\quad {{of}\quad {\sum\limits_{j = 0}^{n - 1}b_{i,j}}}} - \frac{n}{2}$

[0245] divided by m represents the average for the m bits of the wholedigital watermark data. n/2 represents the center of the binarydistribution.

[0246] If the formula (4) is true, it is judged that there is digitalwatermark data. Thus, in each n bit watermark sequence of m digitalwatermark data sequences, digital watermark data is reconstituted by amajority decision processing.

[0247] Specifically, if it is judged that there is digital watermarkdata, digital watermark data is reconstituted in the following way instep 6.

[0248] For all i (0≦i<m),${{{{{when}\quad {\sum\limits_{j = 0}^{n - 1}b_{i,j}}} < {n/2}}:w_{i}^{\prime}} = 0},{{{{{when}\quad {\sum\limits_{j = 0}^{n - 1}b_{i,j}}} \geq {n/2}}:w_{i}^{\prime}} = 1.}$

[0249] This process is carried out by steps 6-1-6-7 in FIG. 25.${{{If}\quad {F\left( {\frac{\sum\limits_{i = 0}^{m - 1}{{{\sum\limits_{j = 0}^{n - 1}b_{i,j}} - \frac{n}{2}}}}{m} + \frac{n}{2}} \right)}} < \alpha},$

[0250] it is judged that there is no watermark data or the presence orabsence is unknown. A following formula (5) can be used instead of theformula (4). $\begin{matrix}{{F\left( {\frac{n}{2} - \frac{\sum\limits_{i = 0}^{m - 1}{{{\sum\limits_{j = 0}^{n - 1}b_{i,j}^{\prime}} - \frac{n}{2}}}}{m}} \right)} \leq {1 - \alpha}} & (5)\end{matrix}$

[0251] If the formula (5) is not true, it is judged that there is nowatermark data or the presence or absence unknown.

[0252] According to the tenth embodiment, statistical processing forwhole watermark sequence is carried out so as to judge the presence orabsence of watermark by using the formula (4) or the formula (5). If itis judged that there is digital watermark data, the reconstitution iscarried out by the majority decision processing. Therefore, even ifthere is one bit of low reliability, digital watermark data can bereconstituted.

[0253] In FIG. 25, the step 1 can be carried out between the steps 4 and5.

[0254] The tenth embodiment may use the pseudo-random sequence which isdescribed in the eighth embodiment. Specifically, watermark embedding iscarried out by modulating digital watermark data sequence with thepseudo-random sequence. When reconstituting, the read digital watermarkdata sequence is demodulated by the pseudo-random sequence, then thejudgment by the formula (4) is performed. If the result is more than αand there is digital watermark data, the reconstitution process of themajority decision is performed on the demodulated sequence, which is thesame process as the step 6 of the eleventh embodiment. The whole processis shown in FIG. 26, adding the same reference symbol to thecorresponding part shown in FIG. 25. In the example, the pseudo-randomsequence {r_(i,j)} is generated from key data ‘Key’ and the process goesto step 2 in step 8. Next to step 4, watermark sequence is demodulatedwith the pseudo-random sequence {r_(i,j)} in step 9. The watermark bitb′_(i,j) in the formula (4) in step 5 is a bit which is demodulated instep 9. Also, the majority decision processing in step 6 is performed onb′_(i,j).

[0255] (Eleventh Embodiment)

[0256] In the following, a eleventh embodiment will be described.

[0257] Since digital watermark data is dispersed by the pseudo-randomsequence, when q is approximated to ½, the presence or the absence ofwatermark data in the watermark sequence can be judged as follows.

[0258] The probability that x bits of ‘1’ (a number x of ‘1’ bits) areincluded in the n bit watermark sequence which constitutes each bit ofdigital watermark data is represented as${F(X)} = {\sum\limits_{j = 0}^{x}{{{}_{}^{}{}_{}^{}}\left( {1/2^{n}} \right)}}$

[0259] by using the binary distribution function. Accordingly, byobtaining the smallest integer X₁ which satisfies F(x=x₁)≧α, thedemodulated sequence of the step 5 in the tenth embodiment can be judgedwith the following formula (6). $\begin{matrix}{{\frac{\sum\limits_{i = 0}^{m - 1}{{{\sum\limits_{j = 0}^{n - 1}b_{i,j}^{\prime}} - \frac{n}{2}}}}{m} + \frac{n}{2}} \geq x_{1}} & (6)\end{matrix}$

[0260] In this case, the amount of processing can be reduced to the samelevel as that of the majority decision processing.

[0261] The judgment is equivalent to a judgment for judging whether theaverage of the bias from the center n/2 of the binary distribution ofthe watermark sequence is equal to or more than X₁.

[0262] If the formula (6) is true and it is judged that there is digitalwatermark data, the majority decision process is performed on thewatermark sequence which is demodulated by the pseudo-random sequence inthe following way.

[0263] For all i (0≦i<m),${{{{{when}\quad {\sum\limits_{j = 0}^{n - 1}b_{i,j}^{\prime}}} < {n/2}}:w_{i}^{\prime}} = 0},{{{{{when}\quad {\sum\limits_{j = 0}^{n - 1}b_{i,j}^{\prime}}} > {n/2}}:w_{i}^{\prime}} = 1}$

[0264] Then, the digital watermark data is reconstituted.${{{{If}\quad \frac{\sum\limits_{i = 0}^{m - 1}{{{\sum\limits_{j = 0}^{n - 1}b_{i,j}^{\prime}} - \frac{n}{2}}}}{m}} + \frac{n}{2}} < x_{1}},$

[0265] it is judged that there is no watermark data or the presence orabsence is unknown.

[0266] In the above process, it is possible to use the maximum integerX₀ which satisfies F(x=x₀)≦1−α instead of the minimum integer X₁ whichsatisfies F(x=x₁)≧α. In this case, a formula for judging the presence orabsence of watermark is shown below as a formula (7). $\begin{matrix}{{\frac{n}{2} - \frac{\sum\limits_{i = 0}^{m - 1}{{{\sum\limits_{j = 0}^{n - 1}b_{i,j}^{\prime}} - \frac{n}{2}}}}{m}} \leq x_{0}} & (7)\end{matrix}$

[0267] If the left part of the formula is more than X₀, it is judgedthat there is no watermark data or the presence or absence is unknown.

[0268] (Twelfth Embodiment)

[0269] In the following, a twelfth embodiment of the present inventionwill be described.

[0270] When it is judged that there is digital watermark data by theformula (4), the digital watermark data is reconstituted by theabove-mentioned majority decision process. At the same time, thereliability of the reconstituted watermark sequence as a whole iscalculated as$F\left( {\frac{\sum\limits_{i = 0}^{m - 1}{{{\sum\limits_{j = 0}^{n - 1}b_{i,j}^{\prime}} - \frac{n}{2}}}}{m} + \frac{n}{2}} \right)$

[0271] and it is output.

[0272] Similarly, when it is judged that there is digital watermark databy the formula (5) and the digital watermark data is reconstituted, thereliability of the reconstituted digital watermark data sequence as awhole is calculated as$F\left( {\frac{n}{2} - \frac{\sum\limits_{i = 0}^{m - 1}{{{\sum\limits_{j = 0}^{n - 1}b_{i,j}^{\prime}} - \frac{n}{2}}}}{m}} \right)$

[0273] and it is output.

[0274] When it is judged that there is digital watermark data by theformula (6), the digital watermark data is reconstituted by theabove-mentioned majority decision process. At the same time, thereliability of the reconstituted watermark sequence as a whole iscalculated as$F\left( {\frac{\sum\limits_{i = 0}^{m - 1}{{{\sum\limits_{j = 0}^{n - 1}b_{i,j}^{\prime}} - \frac{n}{2}}}}{m} + \frac{n}{2}} \right)$

[0275] and it is output.

[0276] Similarly, when it is judged that there is digital watermark databy the formula (7), the reliability of the digital watermark data as awhole is calculated as$F\left( {\frac{n}{2} - \frac{\sum\limits_{i = 0}^{m - 1}{{{\sum\limits_{j = 0}^{n - 1}b_{i,j}^{\prime}} - \frac{n}{2}}}}{m}} \right)$

[0277] and it is output.

[0278] In the above-mentioned seventh-twelfth embodiments, the readingprobability of bit 1 and the number of bit 1 are obtained. However, itis possible that the reading probability of bit 0 and the number of bit0 are obtained. Basically, there is no difference between the former andthe latter. The difference is only on implementation.

[0279] In the following, examples of experiments will be shown. In thefollowing experiments, an image of “lena” which has 128×128 pixels isused as a test image, and the threshold value α of the reliability isassumed to be 0.999999.

[0280] (First Experiment)

[0281] In this experiment, 1 bit digital watermark data ‘1’ was embedded127 times repeatedly using key data ‘50,000’, and the watermark sequencewas read with various key data. FIG. 27 shows the number of bit ‘1’ inthe read watermark sequence corresponding to the key data. In FIG. 27,the vertical axis shows the number of bit ‘1’ in the read watermarksequence, and the horizontal axis shows the key data value. In thisexperiment, the appearance frequency of bit ‘1’ in the watermark area Awas q=0.492247.

[0282] When correct key data (50,000) is used, it is judged that digitalwatermark data is ‘1’ with 99.9999% correctness since the number of bit‘1’ is more than the threshold value X₁ for judging the presence ofwatermark. When incorrect key data is used, it is judged that there isno watermark data or the presence or absence is unknown.

[0283] (Second Experiment)

[0284] In the second experiment, a watermark sequence which wasmodulated with a 7 stage M-sequence (initial state is 64) was embedded,and a similar experiment as the first experiment was carried out withvarious key data and M-sequences of various initial states. The resultis shown in FIG. 28. By carrying out the modulation, the value of qbecomes 0.500000 from 0.492247, and the variance becomes 31.718777 from31.008265. Thus, the values are almost not changed from those of thefirst experiment. It is only when correct key data and correctpseudo-random sequence are used that digital watermark data can be read.In addition, when the watermark sequence is embedded in half data of thewatermark area A, q=0.741547 with the modulation and q=0.499768 withoutthe modulation.

[0285] The effects of the present invention corresponding to the secondobject is as follows.

[0286] (1) There are following effects by judging digital watermark dataon the basis of the binary distribution in statistics:

[0287] The probabilities of following cases can be evaluatedquantitatively. The cases are: digital data contents which do notcontain digital watermark data are wrongly judged as containing digitalwatermark data, and incorrect digital watermark data is read fromwatermarked digital data contents. In addition, the probability can besuppressed within 2(1−α) by using the reliability threshold α of digitalwatermark data.

[0288] (2) There are following effects by modulating digital watermarkdata by a pseudo-random sequence before embedding the digital watermarkdata:

[0289] The bias of the probability q of reading bit ‘1’ when 1 bitwatermark sequence is read at random from the whole watermark area.

[0290] It becomes difficult to detect the presence or absence ofwatermark data and the value from the bias of q without the correct keydata and the pseudo-random sequence, the key data being necessary forreading digital watermark data and the pseudo-random sequence beingnecessary for demodulating read watermark sequence. It can strengthensecurity which is an important element for the digital watermarkingsystem.

[0291] In an implementation, since it can be assumed to be q=½, theamount of processing that is required for watermark reconstitutionbecomes the same as that for majority decision processing. Thus, thespeed of the processing becomes higher.

[0292] α is an index which represents a lower limit of the correctnessrate of read digital watermark data, and is manageable in the digitalwatermarking system. Therefor, the method of using α is superior to aconventional method of showing the correctness rate of read digitalwatermark data to a user.

[0293] According to the seventh embodiment, if there is even one bit oflow reliability in digital watermark data {w′_(i)}, it is judged thatthere is no watermark data or the presence or absence is unknown.However, even in the case, according to the eleventh-thirteenthembodiments, the reliability of digital watermark data can be evaluatedquantitatively, the probability for reading digital watermark dataincorrectly can be suppressed within 2(1−α), and the digital watermarkdata can be reconstituted. In the tenth-twelfth embodiments, the wholedigital watermark data is statistically processed by modifying theformula for judging the presence or absence of digital watermark data,since digital watermark data can be reconstituted in many cases, whenwatermark sequence {b′_(i,j)}, (0≦i<m,0≦j<n) is seen statistically as awhole.

[0294] In addition, according to the seventh embodiment,$F\left( {\sum\limits_{j = 0}^{n - 1}b_{i,j}^{\prime}} \right)$

[0295] needs to be calculated with the distribution function F(x) of thebinary distribution for all i to reconstitute digital watermark datafrom watermark sequence. On the other hand, according to thetenth-twelfth embodiments, only one calculation using the distributionfunction is necessary so that the amount of processing can be reduced.

[0296] The present invention becomes more effective in combination withan error correction code. That is, when a part of bits in digitalwatermark data is intensively corrupted, it is judged that only the partof bits is unknown and other bit data is in high correctness rate.Therefore, correct data can be read by correcting only the corrupted bitdata.

[0297] In the present invention corresponding to the second object, theabove-mentioned processes can be constituted by programs which can bestored in a computer readable medium. Therefore, digital watermarkingprocessing of the present invention can be carried out with a computersuch as one shown in FIG. 17. Additionally, the watermarking apparatusof the present invention can be realized by an integrated circuit suchas one shown in FIG. 18.

[0298] In the following, the present invention corresponding to thethird object will be described.

[0299] In the first place, the conventional digital watermark readingmethod will be further described in order to clarify the feature of thepresent invention corresponding to the first objective. The conventionalmethod is based on hard decisions on binary coding in code theory, whichis shown in FIG. 29. With respect to the watermark reading method basedon hard decisions on binary coding, if almost all watermarked contentsare embedded within a same range (shown as the diagonally shaded area),the performance is enough.

[0300] However, according to the conventional watermark reading method,there is a following problem. FIG. 30 shows a graph showing how MPEG-1coding changes ‘1’ data bit, specifically the graph shows occurrencefrequency with respect to change amount of a DCT coefficient value by1.5 Mbps MPEG-1 coding. As shown in FIG. 30, there is a case in which aconsiderable amount of watermarked data appears in the vicinity of theboundary of the reading bit value (which is shown in two dotted circlesa and a′). As a result, it becomes difficult to separate noise from thewatermarked data. In addition, there is a possibility that a digitalwatermark data value which is read becomes reversed with respect to theembedded digital watermark data.

[0301] In order to avoid the problem, two measures are conceivable.First measure is to raise the data diffusion rate by increasing thenumber of times the data is embedded. Second measure is to increase thewatermark embedding strength. Neither of these measures is a truesolution because the first one may reduce the relative amount ofembedded data and the second one may degrade the image. Accordingly, thepresent invention adopts soft decision rather than hard decision. In thefollowing, a general description of the present invention will be given.

[0302]FIG. 31 is a diagram of a principle of the present inventioncorresponding to the third object. As shown in the figure, a watermarksequence and the reliability is obtained in step 1, and, then, mostlikely digital watermark data is reconstituted based on the watermarksequence and the reliability in step 2.

[0303]FIG. 32 is a diagram showing a principle of a digital watermarkreading apparatus of the present invention. As shown in FIG. 32, thedigital watermark reading apparatus includes a digital watermarksequence obtaining part 1 and reconstitution part 2. The digitalwatermark sequence obtaining part 1 obtains the most likely digitalwatermark sequence and the reliability by carrying out soft decisions ofcoding theory using a weight function, and the reconstitution part 2reconstitutes digital watermark data on the basis of the most likelydigital watermark sequence and the reliability.

[0304] Inferring from the frequency plot shown in FIG. 30, it is easy todetect the digital watermark data sequence correctly if the repeatingnumber of embedding is large enough. However, if a sufficiently largerepeating number can not be obtained in actual practice, it becomesdifficult to detect the desired digital watermark data sequence, thusfiltering for watermarked content data becomes important. For example,concerning data which exists in the dotted circle in FIG. 30, it isdifficult to determine whether the data is watermarked content data ornoise. Thus, it is needed to separate watermarked content data fromnoise effectively. For that purpose, according to the present invention,weights are assigned to the digital watermark data sequence by usingsoft decisions of coding theory. Specifically, distribution ofwatermarked content data is predicted, then digital watermark data isreconstituted from a digital watermark data sequence to which acorresponding distribution value is added as the weight.

[0305] Accordingly, the watermarked content data can be separated fromnoise. Thus, error bits included in the digital watermark data sequencecan be reduced, thereby a success rate of reading digital watermark dataimproves as compared with the above-mentioned conventional methods.According to the present invention, it becomes possible to seesignificant distribution bias in the watermark content data when therepeating number of embedding digital watermark data is small.

[0306] In the following, the present invention corresponding to thethird object will be described in detail.

[0307] First, the operation of the digital watermark reading apparatus106 will be described. FIG. 33 is a diagram for explaining theoperation. As shown in FIG. 33, the process according to the presentinvention corresponds to the process shown in FIG. 5 in which steps240-250 are improved.

[0308] As shown in FIG. 33, in the digital watermark reading apparatus106, when reading digital watermark,${{{v\lbrack X\rbrack}\lbrack Y\rbrack} = {{{weight}\quad \left( \frac{f^{\prime}\lbrack Y\rbrack}{q\lbrack i\rbrack} \right)} - {Z \times \left\{ {\left( {Z\quad {mod}\quad 2} \right) - 1} \right\}}}},$

[0309] for all i$\left( {0 \leq i < {\left\lfloor \frac{m}{n} \right\rfloor \cdot n}} \right),$

[0310] by using frequency coefficient quantization width q[0],q[1], . .. ,q[m−1]. Here,${X = \left\lfloor \frac{i}{t} \right\rfloor},\quad {Y = {i\quad {mod}\quad t}},\quad {Z = {\left\lfloor {\frac{f^{\prime}\lbrack i\rbrack}{q\lbrack i\rbrack} + \frac{1}{2}} \right\rfloor.}}$

[0311] The function weight will be described later.

[0312] In the process for reconstituting digital watermark data byperforming statistical processing on a digital watermark data sequence,for example, ${W\lbrack j\rbrack} = \left\{ {\begin{matrix}1 & {{\sum\limits_{k = 0}^{t - 1}{{v\lbrack j\rbrack}\lbrack k\rbrack}} \geq 0} \\0 & {{\sum\limits_{k = 0}^{t - 1}{{v\lbrack j\rbrack}\lbrack k\rbrack}} < 0}\end{matrix}\quad \left( {0 \leqq j < n} \right)} \right.$

[0313] is used for the reconstitution.

[0314] (Thirteenth Embodiment)

[0315] In the following, a thirteenth embodiment of the presentinvention will be described. In the following example, the digitalwatermark reading process based on quantization in the digital watermarkreading apparatus 106 will be described.

[0316] According to the thirteenth embodiment of the present invention,the digital watermark embedding process is not changed from theconventional method. On the other hand, the digital watermark readingprocess is modified in order to improve digital watermark readingperformance.

[0317] Here, let digital watermark data to be embedded in contents bew₀,w₁, . . . ,w_(n−1),w_(i) ε{−1,1}, 0≦i≦n−1, and let a data set inwhich digital watermark data is embedded be {d_(0,0),d_(0,1), . . .,d_(0,m−1),d_(1,0),d_(1,1), . . . ,d_(1,m−1), . . . ,d_(n−1,1) . . .,d_(n−1,m−1)}. Let a quantization value used for quantize data d_(i,j)(0≦i≦n−1,0≦j≦m−1) be q_(i,j). Each bit data W_(i) of digital watermarkdata is embedded m times repeatedly. The digital watermark embeddingprocess based on quantization is assumed to be a process in thefollowing.

[0318] For all i and j (0≦i≦n−1, 0≦j≦m−1)${{\left. i \right)\quad {If}\quad \left\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \right\rfloor \quad {mod}\quad 2\quad {is}\quad {equal}\quad {to}\quad w_{i}},{d_{i,j}\quad {is}\quad {changed}\quad {to}\quad \left\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \right\rfloor \quad \times {q_{i,j}.{ii}}\text{)}\quad {If}\quad \left\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \right\rfloor \quad {mod}{\quad \quad}2\quad {is}\quad {different}\quad {from}\quad w_{i}\quad {and}\quad \left\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \right\rfloor \quad {is}\quad {equal}\quad {to}\quad \left\lfloor \frac{d_{i,j}}{q_{i,j}} \right\rfloor},{d_{i,j}\quad {is}\quad {changed}\quad {to}\quad \left( \quad {\left\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \right\rfloor \quad + 1} \right) \times {q_{i,j}.\quad {iii}}\text{)}\quad {If}\quad \left\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \right\rfloor \quad {mod}\quad 2\quad {is}\quad {different}\quad {from}\quad w_{i}\quad {and}{\quad \quad}\left\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \right\rfloor \quad {is}\quad {different}\quad {from}\quad \left\lfloor \frac{d_{i,j}}{q_{i,j}} \right\rfloor},{d_{i,j}\quad {is}\quad {changed}\quad {to}\quad \left( \quad {\left\lfloor {\frac{d_{i,j}}{q_{i,j}} + \frac{1}{2}} \right\rfloor \quad - 1} \right) \times {q_{i,j}.}}}\quad$

[0319] Here, └x┘ is a maximum number which does not exceed x. “x mod y”represents the remainder of x divided by y.

[0320] The present invention is not only applicable to the contents inwhich digital watermark data is embedded in the above-mentioned way butalso applicable to other contents in which digital watermark data isembedded in other equivalent way.

[0321] In the following, the operation of the digital watermark readingapparatus 106 will be described in detail.

[0322] According to a following process, a watermark sequence {{tildeover (w)}_(0,0), {tilde over (w)}_(0,1), . . . , {tilde over(w)}_(0,m−1), {tilde over (w)}_(1,0), {tilde over (w)}_(1,1), . . . ,{tilde over (w)}_(1,m−1), . . . , {tilde over (w)}_(n−1,0), {tilde over(w)}_(n−1,1), . . . , {tilde over (w)}_(n−1,m−1)} is read from a set ofdata values {{tilde over (d)}_(0,0), {tilde over (d)}_(0,1), . . . ,{tilde over (d)}_(0,m−1), {tilde over (d)}_(1,0), {tilde over(d)}_(1,1), . . . , {tilde over (d)}_(1,m−1), . . . , {tilde over(d)}_(n−1,0), {tilde over (d)}_(n−1,1), . . . , {tilde over(d)}_(n−1,m−1)} of the watermarked digital data contents 105 in whichdigital watermark data is embedded.

[0323] For all i and j (0≦i≦n−1, 0≦j≦m−1)${n_{i,j} = \quad {\left\lfloor {\frac{{\overset{\sim}{d}}_{i,j}}{q_{i,j}} + \frac{1}{2}} \right\rfloor \quad {and}}}\quad$${\overset{\sim}{w}}_{i,j} = {{weight}\quad \left( {\frac{{\overset{\sim}{d}}_{i,j}}{q_{i,j}} - n_{i,j}} \right) \times {\left\{ {{\left( {n_{i,j}\quad {mod}\quad 2} \right) \times 2} - 1} \right\}.}}$

[0324] Here, weight(x) (the domain is${{- \frac{1}{2}} \leq x \leq \frac{1}{2}},$

[0325] and the range is equal to or more than 0. The function weight(x)will be called a weight function hereinafter) is a function whichassigns weights to a read watermark sequence. By adopting a functionwhich takes a large value in the vicinity of the central value (in thevicinity of the dotted vertical axis in FIG. 30) and takes a small valuein the vicinity of the boundary of the bit value (in the dotted circlein FIG. 30), it becomes possible to separate effective watermark datasequence from noise.

[0326] Of course, it is possible to adopt a stretched weight(x) functionin which the domain and the region is not limited. However, in the case,it is necessary to change the above mentioned formula to some extent.

[0327] Contents in which digital watermark data is embedded by digitalwatermark embedding processing is degraded due to data compression,media processing and the like. Thus, a watermark embedded data value{tilde over (d)}_(i,j) deviates in some degree from a value d_(i,j) ofimmediately after being embedded. Therefore, it is desirable to adopt afollowing function as the weight function. The function can be obtainedsuch that the distribution of the ratio$\frac{{\overset{\sim}{d}}_{i,j} - d}{q_{i,j}}$

[0328] of the amount of the deviation between d_(i,j) and {tilde over(d)}_(i,j) to the quantization value q_(i,j) is predicted, and it isnormalized with an appropriate scale for approximation. (There is nocondition for the scale.)

[0329] For example, when assuming that digital watermark data is readfrom watermarked motion pictures which are MPEG compressed, thedistribution shown in FIG. 30 can be approximated by a Laplaciandistribution. Thus, a Laplacian distribution of average 0 and variance0.08 or a normal distribution of average 0 and variance {fraction(1/16)} can be used effectively as the weighting function.

[0330] In addition, there is another method which uses anotherdistribution function. The distribution function is formed so as topredict the error of the watermarked content data.

[0331] The digital watermark reading apparatus 106 reconstitutes andoutputs digital watermark data {tilde over (w)}₀, {tilde over (w)}₁, . .. , {tilde over (w)}_(n−1) from read watermark sequence by applying, forexample, $w_{i} = \left\{ \begin{matrix}1 & {{\sum\limits_{j = 0}^{m - 1}{\overset{\sim}{w}}_{i,j}} \geq 0} \\{- 1} & {{\sum\limits_{j = 0}^{m - 1}{\overset{\sim}{w}}_{i,j}} < 0}\end{matrix} \right.$

[0332] or Japanese patent application No.10-219236, “Embedding datacoding method, the apparatus, computer readable medium storing embeddingdata coding program, read data decoding method, the apparatus, computerreadable medium storing read data decoding program, digital watermarkdata coding method, the apparatus, computer readable medium storingdigital watermark coding program, digital watermark decoding method, theapparatus, computer readable medium storing digital watermark decodingprogram”.

[0333] In addition, the above-mentioned process performed by the digitalwatermark reading apparatus 106 can be constructed by a program whichcan be stored in a computer readable medium such as a disk unit, afloppy disk, CD-ROM and the like. That is, by installing the program ina computer such as one shown in FIG. 17, the processes of watermarkreading of the present invention can be carried out. In addition, thedigital watermark reading apparatus of the present invention can berealized by the integrated circuit shown in FIG. 18.

[0334] Experiments is performed in order to compare the method of thepresent invention and the conventional method of digital watermarking tomotion pictures described in Japanese patent application No.9-164466.

[0335] As experimental conditions, a unit for digital watermarkprocessing is assumed to be a 16×16 pixel and the conventional digitalwatermark data sequence reading is assumed to be {tilde over(w)}_(i,j)=(n_(i,j) mod 2)×2−1 on the basis of the assumptions of theabove-mentioned embodiment. Watermark data is reconstituted as {tildeover (w)}₀, w₁, . . . , w_(n−1) for both of the present invention andthe conventional method.

[0336] As shown in FIG. 34, it is recognized that digital watermark datareading success rate is improved in an MPEG-1 coded picture in any bitrates. The result shows the effectiveness of the present invention.Here, the digital watermark data reading success rate is obtained bydividing the number of correctly reconstituted digital watermark data bythe total number of embedded digital watermark data.

[0337] According to the present invention, the digital watermark datasequence is separated from the noise so that error bits which areincluded in the digital watermark data sequence can be reduced, therebythe digital watermark data reading success rate is improved incomparison with the conventional method.

[0338] In addition, since weights are assigned to the digital watermarkdata sequence, the present invention is especially effective when therepeating number of watermark embedding is small.

[0339] The point of the present invention corresponding to the thirdobjective is applying soft decisions for the digital watermark readingprocess as opposed to the conventional method which uses hard decisions.The present invention is not limited to the above-mentioned process andcan apply to other equivalent digital watermarking method.

[0340] In the above-mentioned embodiments corresponding to first-thirdobjects, embodiments corresponding to each object can be performed withembodiments corresponding to other objects.

[0341] The present invention is not limited to the specificallydisclosed embodiments, and variations and modifications may be madewithout departing from the scope of the invention.

What is claimed is:
 1. A method for embedding digital watermark data indigital data contents, said method comprising the steps of: receivingsaid digital data contents and said digital watermark data; dividingsaid digital data contents into block data; obtaining a frequencycoefficient of said block data; obtaining a complexity of said blockdata; obtaining an amount of transformation of said frequencycoefficient from said complexity and said digital watermark data byusing a quantization width; embedding said digital watermark data insaid digital data contents by transforming said frequency coefficient bysaid amount; and generating watermarked digital data contents.
 2. Themethod as claimed in claim 1, said step of obtaining said complexity ofsaid block data comprising the steps of: transforming said block data,by applying a wavelet transform, into coefficients of said wavelettransform, and obtaining said complexity on the basis of the number ofhigh frequency coefficients in said coefficients of said wavelettransform, each of said high frequency coefficients exceeding athreshold.
 3. A method for embedding digital watermark data in digitaldata contents, said method comprising the steps of: receiving saiddigital data contents and said digital watermark data; dividing saiddigital data contents into block data; obtaining a frequency coefficientof said block data; obtaining an amount of transformation of saidfrequency coefficient from said digital watermark data by using aquantization width corresponding to said frequency coefficient, saidquantization width being obtained beforehand according to a manipulationmethod of said digital data contents; embedding said digital watermarkdata in said digital data contents by transforming said frequencycoefficient by said amount; and generating watermarked digital datacontents.
 4. The method as claimed in claim 3, wherein said quantizationwidth is obtained by a method comprising the steps of: dividing firstdigital data contents into one or a plurality of first block data;dividing second digital data contents into one or a plurality of secondblock data, said second digital data contents being obtained bymanipulating said first digital data contents with a predeterminedmanipulation method; transforming said first block data and said secondblock data into first frequency coefficients and second frequencycoefficients respectively by applying an orthogonal transform; obtainingdifference values between said first frequency coefficients and saidsecond frequency coefficients for each frequency coefficient;calculating a standard deviation of distribution of said differencevalues; and obtaining said quantization width by multiplying saidstandard deviation by a watermark embedding strength.
 5. A method forreading digital watermark data embedded in digital data contents, saidmethod comprising the steps of: receiving said digital data contents;dividing said digital data contents into block data; obtaining afrequency coefficient of said block data; and generating digitalwatermark data from said frequency coefficient by using a quantizationwidth corresponding to said frequency coefficient, said quantizationwidth being obtained beforehand according to a manipulation method ofsaid digital data contents.
 6. The method as claimed in claim 5, whereinsaid quantization width is obtained by a method comprising the steps of:dividing first digital data contents into one or a plurality of firstblock data; dividing second digital data contents into one or aplurality of second block data, said second digital data contents beingobtained by manipulating said first digital data contents with apredetermined manipulation method; transforming said first block dataand said second block data into first frequency coefficients and secondfrequency coefficients respectively by applying an orthogonal transform;obtaining difference values between said first frequency coefficientsand said second frequency coefficients for each frequency coefficient;calculating a standard deviation of distribution of said differencevalues; and obtaining said quantization width by multiplying saidstandard deviation by a watermark embedding strength.
 7. An apparatusfor embedding digital watermark data in digital data contents, saidapparatus comprising: means for receiving said digital data contents andsaid digital watermark data; means for dividing said digital datacontents into block data; means for obtaining a frequency coefficient ofsaid block data; means for obtaining a complexity of said block data;means for obtaining an amount of transformation of said frequencycoefficient from said complexity and said digital watermark data byusing a quantization width; means for embedding said digital watermarkdata in said digital data contents by transforming said frequencycoefficient by said amount; and means for generating watermarked digitaldata contents.
 8. The apparatus as claimed in claim 7, said means forobtaining said complexity of said block data comprising: means fortransforming said block data, by applying a wavelet transform, intocoefficients of said wavelet transform, and means for obtaining saidcomplexity on the basis of the number of high frequency coefficients insaid coefficients of said wavelet transform, each of said high frequencycoefficients exceeding a threshold.
 9. An apparatus for embeddingdigital watermark data in digital data contents, said apparatuscomprising: means for receiving said digital data contents and saiddigital watermark data; means for dividing said digital data contentsinto block data; means for obtaining a frequency coefficient of saidblock data; means for obtaining an amount of transformation of saidfrequency coefficient from said digital watermark data by using aquantization width corresponding to said frequency coefficient, saidquantization width being obtained beforehand according to a manipulationmethod of said digital data contents; means for embedding said digitalwatermark data in said digital data contents by transforming saidfrequency coefficient by said amount; and means for generatingwatermarked digital data contents.
 10. The apparatus as claimed in claim9, wherein said quantization width is obtained by means comprising:means for dividing first digital data contents into one or a pluralityof first block data; means for dividing second digital data contentsinto one or a plurality of second block data, said second digital datacontents being obtained by manipulating said first digital data contentswith a predetermined manipulation method; means for transforming saidfirst block data and said second block data into first frequencycoefficients and second frequency coefficients respectively by applyingan orthogonal transform; means for obtaining difference values betweensaid first frequency coefficients and said second frequency coefficientsfor each frequency coefficient; means for calculating a standarddeviation of distribution of said difference values; and means forobtaining said quantization width by multiplying said standard deviationby a watermark embedding strength.
 11. An apparatus for reading digitalwatermark data embedded in digital data contents, said apparatuscomprising: means for receiving said digital data contents; means fordividing said digital data contents into block data; means for obtaininga frequency coefficient of said block data; and means for generatingdigital watermark data from said frequency coefficient by using aquantization width corresponding to said frequency coefficient, saidquantization width being obtained beforehand according to a manipulationmethod of said digital data contents.
 12. The apparatus as claimed inclaim 11, wherein said quantization width is obtained by meanscomprising: means for dividing first digital data contents into one or aplurality of first block data; means for dividing second digital datacontents into one or a plurality of second block data, said seconddigital data contents being obtained by manipulating said first digitaldata contents with a predetermined manipulation method; means fortransforming said first block data and said second block data into firstfrequency coefficients and second frequency coefficients respectively byapplying an orthogonal transform; means for obtaining difference valuesbetween said first frequency coefficients and said second frequencycoefficients for each frequency coefficient; means for calculating astandard deviation of distribution of said difference values; and meansfor obtaining said quantization width by multiplying said standarddeviation by a watermark embedding strength.
 13. An integrated circuitfor embedding digital watermark data in digital data contents, saidintegrated circuit comprising: means for receiving said digital datacontents and said digital watermark data; means for dividing saiddigital data contents into block data; means for obtaining a frequencycoefficient of said block data; means for obtaining a complexity of saidblock data; means for obtaining an amount of transformation of saidfrequency coefficient from said complexity and said digital watermarkdata by using a quantization width; means for embedding said digitalwatermark data in said digital data contents by transforming saidfrequency coefficient by said amount; and means for generatingwatermarked digital data contents.
 14. The integrated circuit as claimedin claim 13, said means for obtaining said complexity of said block datacomprising: means for transforming said block data, by applying awavelet transform, into coefficients of said wavelet transform, andmeans for obtaining said complexity on the basis of the number of highfrequency coefficients in said coefficients of said wavelet transform,each of said high frequency coefficients exceeding a threshold.
 15. Anintegrated circuit for embedding digital watermark data in digital datacontents, said integrated circuit comprising: means for receiving saiddigital data contents and said digital watermark data; means fordividing said digital data contents into block data; means for obtaininga frequency coefficient of said block data; means for obtaining anamount of transformation of said frequency coefficient from said digitalwatermark data by using a quantization width corresponding to saidfrequency coefficient, said quantization width being obtained beforehandaccording to a manipulation method of said digital data contents; meansfor embedding said digital watermark data in said digital data contentsby transforming said frequency coefficient by said amount; and means forgenerating watermarked digital data contents.
 16. The integrated circuitas claimed in claim 15, wherein said quantization width is obtained bymeans comprising: means for dividing first digital data contents intoone or a plurality of first block data; means for dividing seconddigital data contents into one or a plurality of second block data, saidsecond digital data contents being obtained by manipulating said firstdigital data contents with a predetermined manipulation method; meansfor transforming said first block data and said second block data intofirst frequency coefficients and second frequency coefficientsrespectively by applying an orthogonal transform; means for obtainingdifference values between said first frequency coefficients and saidsecond frequency coefficients for each frequency coefficient; means forcalculating a standard deviation of distribution of said differencevalues; and means for obtaining said quantization width by multiplyingsaid standard deviation by a watermark embedding strength.
 17. Anintegrated circuit for reading digital watermark data embedded indigital data contents, said integrated circuit comprising: means forreceiving said digital data contents; means for dividing said digitaldata contents into block data; means for obtaining a frequencycoefficient of said block data; and means for generating digitalwatermark data from said frequency coefficient by using a quantizationwidth corresponding to said frequency coefficient, said quantizationwidth being obtained beforehand according to a manipulation method ofsaid digital data contents.
 18. The integrated circuit as claimed inclaim 17, wherein said quantization width is obtained by meanscomprising: means for dividing first digital data contents into one or aplurality of first block data; means for dividing second digital datacontents into one or a plurality of second block data, said seconddigital data contents being obtained by manipulating said first digitaldata contents with a predetermined manipulation method; means fortransforming said first block data and said second block data into firstfrequency coefficients and second frequency coefficients respectively byapplying an orthogonal transform; means for obtaining difference valuesbetween said first frequency coefficients and said second frequencycoefficients for each frequency coefficient; means for calculating astandard deviation of distribution of said difference values; and meansfor obtaining said quantization width by multiplying said standarddeviation by a watermark embedding strength.
 19. A computer readablemedium storing program code for causing a computer system to embeddigital watermark data in digital data contents, said computer readablemedium comprising: program code means for receiving said digital datacontents and said digital watermark data; program code means fordividing said digital data contents into block data; program code meansfor obtaining a frequency coefficient of said block data; program codemeans for obtaining a complexity of said block data; program code meansfor obtaining an amount of transformation of said frequency coefficientfrom said complexity and said digital watermark data by using aquantization width; program code means for embedding said digitalwatermark data in said digital data contents by transforming saidfrequency coefficient by said amount; and program code means forgenerating watermarked digital data contents.
 20. The computer readablemedium as claimed in claim 19, said program code means for obtainingsaid complexity of said block data comprising: program code means fortransforming said block data, by applying a wavelet transform, intocoefficients of said wavelet transform, and program code means forobtaining said complexity on the basis of the number of high frequencycoefficients in said coefficients of said wavelet transform, each ofsaid high frequency coefficients exceeding a threshold.
 21. A computerreadable medium storing program code for causing a computer system toembed digital watermark data in digital data contents, said computerreadable medium comprising: program code means for receiving saiddigital data contents and said digital watermark data; program codemeans for dividing said digital data contents into block data; programcode means for obtaining a frequency coefficient of said block data;program code means for obtaining an amount of transformation of saidfrequency coefficient from said digital watermark data by using aquantization width corresponding to said frequency coefficient, saidquantization width being obtained beforehand according to a manipulationmethod of said digital data contents; program code means for embeddingsaid digital watermark data in said digital data contents bytransforming said frequency coefficient by said amount; and program codemeans for generating watermarked digital data contents.
 22. The computerreadable medium as claimed in claim 21, wherein said quantization widthis obtained by program code means comprising: program code means fordividing first digital data contents into one or a plurality of firstblock data; program code means for dividing second digital data contentsinto one or a plurality of second block data, said second digital datacontents being obtained by manipulating said first digital data contentswith a predetermined manipulation method; program code means fortransforming said first block data and said second block data into firstfrequency coefficients and second frequency coefficients respectively byapplying an orthogonal transform; program code means for obtainingdifference values between said first frequency coefficients and saidsecond frequency coefficients for each frequency coefficient; programcode means for calculating a standard deviation of distribution of saiddifference values; and program code means for obtaining saidquantization width by multiplying said standard deviation by a watermarkembedding strength.
 23. A computer readable medium storing program codefor causing a computer system to read digital watermark data embedded indigital data contents, said computer readable medium comprising: programcode means for receiving said digital data contents; program code meansfor dividing said digital data contents into block data; program codemeans for obtaining a frequency coefficient of said block data; andprogram code means for generating digital watermark data from saidfrequency coefficient by using a quantization width corresponding tosaid frequency coefficient, said quantization width being obtainedbeforehand according to a manipulation method of said digital datacontents.
 24. The computer readable medium as claimed in claim 23,wherein said quantization width is obtained by program code meanscomprising: program code means for dividing first digital data contentsinto one or a plurality of first block data; program code means fordividing second digital data contents into one or a plurality of secondblock data, said second digital data contents being obtained bymanipulating said first digital data contents with a predeterminedmanipulation method; program code means for transforming said firstblock data and said second block data into first frequency coefficientsand second frequency coefficients respectively by applying an orthogonaltransform; program code means for obtaining difference values betweensaid first frequency coefficients and said second frequency coefficientsfor each frequency coefficient; program code means for calculating astandard deviation of distribution of said difference values; andprogram code means for obtaining said quantization width by multiplyingsaid standard deviation by a watermark embedding strength.
 25. A methodfor reading digital watermark data embedded in digital data contents,said method comprising the steps of: receiving said digital datacontents; reading a bit sequence from said digital data contents;calculating a probability of reading a bit ‘1’ or a bit ‘0’ in said bitsequence by using a test method on the basis of binary distribution;determining the presence or absence of digital watermark data accordingto said probability; and reconstituting and generating said digitalwatermark data from said bit sequence.
 26. The method as claimed inclaim 25, further comprising the steps of: determining threshold α ofreliability of digital watermark data which is read; obtaining a binarydistribution function F(x) which represents a probability that a numberx of ‘1’ bits or ‘0’ bits are included in a bit sequence which is readat random from digital data contents, said binary distribution functionF(x) being obtained by using a probability q of reading ‘1’ or ‘0’ insaid bit sequence and a repeating number of embedding each bit ofdigital watermark data; reading an ith digital watermark sequence ofsaid digital watermark data from a digital watermark area of saiddigital data contents; calculating the number k_(i) of ‘1’ or ‘0’included in said digital watermark sequence; calculating a probabilityF(k_(i)) by using said binary distribution function F(x); andreconstituting ‘1’ or ‘0’ from ith digital watermark data w_(i) ifF(k_(i))>α, reconstituting ‘0’ or ‘1’ from ith digital watermark dataw_(i) if 1−F(k_(i))>α, and determining that there is no watermark dataor the presence is unknown if both of F(k_(i))>α and 1−F(k_(i))>α arenot satisfied.
 27. The method as claimed in claim 26, further comprisingthe steps of: outputting F(k_(i)) as reliability if said reconstituteddigital watermark data w_(i) is ‘1’; and outputting 1−F(k_(i)) as thereliability if said reconstituted digital watermark data w_(i) is ‘0’.28. The method as claimed in claim 25, further comprising the steps of:determining a threshold α of reliability of digital watermark data whichis read; obtaining a binary distribution function F(x) which representsa probability that a number x of ‘1’ bits or ‘0’ bits are included in abit sequence which is read at random from digital data contents, saidbinary distribution function F(x) being obtained by using a probabilityq of reading ‘1’ or ‘0’ in said bit sequence and a repeating number ofembedding each bit of digital watermark data; reading an ith digitalwatermark sequence of said digital watermark data from a digitalwatermark area of said digital data contents; checking whether aprobability that said digital watermark sequence is digital watermarkdata exceeds said threshold α by using said binary distribution functionF(x); and reconstituting digital watermark data from said digitalwatermark sequence by using majority decision processing if saidprobability exceeds α, and determining that there is no watermark dataor the presence is unknown if said probability does not exceed α. 29.The method as claimed in claim 28, further comprising a step ofoutputting said probability that said digital watermark sequence isdigital watermark data.
 30. The method as claimed in claim 25, if a datasequence which is embedded as said digital watermark data is modulatedby a pseudo-random sequence, said method further comprising the stepsof: demodulating said bit sequence by said pseudo-random sequence; andreconstituting digital watermark data from said demodulated bitsequence.
 31. The method as claimed in claim 25, if a data sequencewhich is embedded as said digital watermark data is modulated by apseudo-random sequence, said method further comprising the steps of:determining a threshold α of reliability of digital watermark data whichis read; obtaining a binary distribution function F(x) which representsa probability that a number of x of ‘1’ bits or ‘0’ bits are included ina bit sequence which is read at random from digital data contents, saidbinary distribution function F(x) being obtained by using a probabilityq of reading ‘1’ or ‘0’ in said bit sequence and a repeating number ofembedding each bit of digital watermark data; reading an ith digitalwatermark sequence of said digital watermark data from a digitalwatermark area of said digital data contents; demodulating said digitalwatermark sequence by said pseudo-random sequence; assigning ½ to saidprobability q; obtaining a maximum number x₀ which satisfies0≦F(x=x₀)≦1−α and a minimum number x₁ which satisfies α≦F(x=x₁)≦1;obtaining the number k_(i) of ‘1’ or ‘0’ included in said ith digitalwatermark sequence; and reconstituting ith digital watermark data w_(i)as ‘0’ or ‘1’ if k_(i)≦x₀, and reconstituting said ith digital watermarkdata w_(i) as ‘1’ or ‘0’ if k_(i)≧x₁.
 32. The method as claimed in claim25, if a data sequence which is embedded as said digital watermark datais modulated by a pseudo-random sequence, said method further comprisingthe steps of: determining a threshold α of reliability of digitalwatermark data which is read; obtaining a binary distribution functionF(x) which represents a probability that x of ‘1’ bits or ‘0’ bits areincluded in a bit sequence which is read at random from digital datacontents, said binary distribution function F(x) being obtained by usinga probability q of reading ‘1’ or ‘0’ in said bit sequence and arepeating number t of embedding each bit of digital watermark data;reading an ith digital watermark sequence of said digital watermark datafrom a digital watermark area of said digital data contents;demodulating said digital watermark sequence by said pseudo-randomsequence; assigning ½ to said probability q; obtaining x₀ or x₁ whichsatisfies 0≦F(x=x₀)≦1−α or α≦F(x=x₁)≦1; determining whether a value isequal to or less than x₀ or equal to or more than x₁, said value being amean value of absolute values of a difference between the number of ‘0’or ‘1’ included in said ith digital watermark sequence and a centralvalue q×t of a binary distribution; reconstituting digital watermarkdata by performing majority decision processing for said ith digitalwatermark sequence if said value is equal to or less than x₀ or equal toor more than x₁; and determining that there is no digital watermark dataor the presence is unknown if said value is not equal to or less than x₀or equal to or more than x₁.
 33. The method as claimed in claim 32,further comprising the steps of: calculating a value of said binarydistribution function F(z), z being said mean value obtained from thenumber of ‘0’ or ‘1’ included in said ith digital watermark sequence andsaid central value q×t; and outputting said value of F(z) as reliabilityof digital watermark data.
 34. An apparatus for reading digitalwatermark data embedded in digital data contents, said apparatuscomprising: means for receiving said digital data contents; means forreading a bit sequence from said digital data contents; means forcalculating a probability of reading a bit ‘1’ or a bit ‘0’ in said bitsequence by using a test method on the basis of binary distribution;means for determining the presence or absence of digital watermark dataaccording to said probability; and means for reconstituting said digitalwatermark data from said bit sequence.
 35. The apparatus as claimed inclaim 34, further comprising: means for obtaining a binary distributionfunction F(x) which represents a probability that a number x of ‘1’ bitsor ‘0’ bits are included in a bit sequence which is read at random fromdigital data contents, said binary distribution function F(x) beingobtained by using a probability q of reading ‘1’ or ‘0’ in said bitsequence and a repeating number of embedding each bit of digitalwatermark data; means for reading an ith digital watermark sequence ofsaid digital watermark data from a digital watermark area of saiddigital data contents; means for calculating the number k_(i) of ‘1’ or‘0’ included in said digital watermark sequence; means for calculating aprobability F(k_(i)) by using said binary distribution function F(x);and means for reconstituting ‘1’ or ‘0’ from ith digital watermark dataw_(i) if F(k_(i))>α, reconstituting ‘0’ or ‘1’ from ith digitalwatermark data w_(i) if 1−F(k_(i))>α, and, determining that there is nowatermark data or the presence is unknown if both of F(k_(i))>α and1−F(k_(i))>α are not satisfied, α being a threshold of reliability ofdigital watermark data which is read.
 36. The apparatus as claimed inclaim 35, further comprising: means for outputting F(k_(i)) asreliability if said reconstituted digital watermark data w_(i) is ‘1’;and means for outputting 1−F(k_(i)) as reliability if said reconstituteddigital watermark data w_(i) is ‘0’.
 37. The apparatus as claimed inclaim 34, further comprising: means for obtaining a binary distributionfunction F(x) which represents a probability that a number x of ‘1’ bitsor ‘0’ bits are included in a bit sequence which is read at random fromdigital data contents, said binary distribution function F(x) beingobtained by using a probability q of reading ‘1’ or ‘0’ in said bitsequence and a repeating number of embedding each bit of digitalwatermark data; means for reading an ith digital watermark sequence ofsaid digital watermark data from a digital watermark area of saiddigital data contents; means for checking whether a probability thatsaid digital watermark sequence is digital watermark data exceeds saidthreshold α by using said binary distribution function F(x), α being athreshold of reliability of digital watermark data which is read; andmeans for reconstituting and generating digital watermark data from saiddigital watermark sequence by using majority decision processing if saidprobability exceeds α, and, determining that there is no watermark dataor the presence is unknown if said probability does not exceed α. 38.The apparatus as claimed in claim 37, further comprising means foroutputting said probability that said digital watermark sequence isdigital watermark data.
 39. The apparatus as claimed in claim 34, if adata sequence which is embedded as said digital watermark data ismodulated by a pseudo-random sequence, said apparatus furthercomprising: means for demodulating said bit sequence by saidpseudo-random sequence; and means for reconstituting digital watermarkdata from said demodulated bit sequence.
 40. The apparatus as claimed inclaim 34, if a data sequence which is embedded as said digital watermarkdata is modulated by a pseudo-random sequence, said apparatus furthercomprising: means for obtaining a binary distribution function F(x)which represents a probability that a number x of ‘1’ bits or ‘0’ bitsare included in a bit sequence which is read at random from digital datacontents, said binary distribution function F(x) being obtained by usinga probability q of reading ‘1’ or ‘0’ in said bit sequence and arepeating number of embedding each bit of digital watermark data; meansfor reading an ith digital watermark sequence of said digital watermarkdata from a digital watermark area of said digital data contents; meansfor demodulating said digital watermark sequence by said pseudo-randomsequence; means for assigning ½ to said probability q; means forobtaining a maximum number x₀ which satisfies 0≦F(x=x₀)≦1−α and aminimum number x₁ which satisfies α≦F(x=x₁)≦1, α being a threshold ofreliability of digital watermark data which is read; means for obtainingthe number k_(i) of ‘1’ or ‘0’ included in said ith digital watermarksequence; and means for reconstituting ith digital watermark data w_(i)as ‘0’ or ‘1’ if k_(i)≦x₀, and, reconstituting said ith digitalwatermark data w_(i) as ‘1’ or ‘0’ if k_(i)≧x₁.
 41. The apparatus asclaimed in claim 34, if a data sequence which is embedded as saiddigital watermark data is modulated by a pseudo-random sequence, saidapparatus further comprising: means for obtaining a binary distributionfunction F(x) which represents a probability that a number x of ‘1’ bitsor ‘0’ bits are included in a bit sequence which is read at random fromdigital data contents, said binary distribution function F(x) beingobtained by using a probability q of reading ‘1’ or ‘0’ in said bitsequence and a repeating number t of embedding each bit of digitalwatermark data; means for reading an ith digital watermark sequence ofsaid digital watermark data from a digital watermark area of saiddigital data contents; means for demodulating said digital watermarksequence by said pseudo-random sequence; means for assigning ½ to saidprobability q; means for obtaining x₀ or x₁ which satisfies0≦F(x=x₀)≦1−α or α≦F(x=x₁)≦1, α being a threshold of reliability ofdigital watermark data which is read; means for determining whether avalue is equal to or less than x₀ or equal to or more than x₁, saidvalue being a mean value of absolute values of a difference between thenumber of ‘0’ or ‘1’ included in said ith digital watermark sequence anda central value q×t of a binary distribution; means for reconstitutingdigital watermark data by performing majority decision processing forsaid ith digital watermark sequence if said value is equal to or lessthan x₀ or equal to or more than x₁; and means for determining thatthere is no digital watermark data or the presence is unknown if saidvalue is not equal to or less than x₀ or equal to or more than x₁. 42.The apparatus as claimed in claim 41, further comprising: means forcalculating a value of said binary distribution function F(z), z beingsaid mean value obtained from the number of ‘0’ or ‘1’ included in saidith digital watermark sequence and said central value q×t; and means foroutputting said value of F(z) as reliability of digital watermark data.43. An integrated circuit for reading digital watermark data embedded indigital data contents, said integrated circuit comprising: means forreceiving said digital data contents; means for reading a bit sequencefrom said digital data contents; means for calculating a probability ofreading a bit ‘1’ or a bit ‘0’ in said bit sequence by using a testmethod on the basis of binary distribution; means for determining thepresence or absence of digital watermark data according to saidprobability; and means for reconstituting and generating said digitalwatermark data from said bit sequence.
 44. The integrated circuit asclaimed in claim 43, further comprising: means for obtaining a binarydistribution function F(x) which represents a probability that a numberx of ‘1’ bits or ‘0’ bits are included in a bit sequence which is readat random from digital data contents, said binary distribution functionF(x) being obtained by using a probability q of reading ‘1’ or ‘0’ insaid bit sequence and a repeating number of embedding each bit ofdigital watermark data; means for reading an ith digital watermarksequence of said digital watermark data from a digital watermark area ofsaid digital data contents; means for calculating the number k_(i) of‘1’ or ‘0’ included in said digital watermark sequence; means forcalculating a probability F(k_(i)) by using said binary distributionfunction F(x); and means for reconstituting ‘1’ or ‘0’ from ith digitalwatermark data w_(i) if F(k_(i))>α, reconstituting ‘0’ or ‘1’ from ithdigital watermark data w_(i) if 1−F(k_(i))>α, and determining that thereis no watermark data or the presence is unknown if both of F(k_(i))>αand 1−F(k_(i))>α are not satisfied, α being a threshold of reliabilityof digital watermark data which is read.
 45. The integrated circuit asclaimed in claim 44, further comprising: means for outputting F(k_(i))as reliability if said reconstituted digital watermark data w_(i) is‘1’; and means for outputting 1−F(k_(i)) as reliability if saidreconstituted digital watermark data w_(i) is ‘0’.
 46. The integratedcircuit as claimed in claim 43, further comprising: means for obtaininga binary distribution function F(x) which represents a probability thata number of x of ‘1’ bits or ‘0’ bits are included in a bit sequencewhich is read at random from digital data contents, said binarydistribution function F(x) being obtained by using a probability q ofreading ‘1’ or ‘0’ in said bit sequence and a repeating number ofembedding each bit of digital watermark data; means for reading an ithdigital watermark sequence of said digital watermark data from a digitalwatermark area of said digital data contents; means for checking whethera probability that said digital watermark sequence is digital watermarkdata exceeds said threshold α by using said binary distribution functionF(x), α being a threshold of reliability of digital watermark data whichis read; and means for reconstituting and generating digital watermarkdata from said digital watermark sequence by using majority decisionprocessing if said probability exceeds α, and, determining that there isno watermark data or the presence is unknown if said probability doesnot exceed α.
 47. The integrated circuit as claimed in claim 46, furthercomprising means for outputting said probability that said digitalwatermark sequence is digital watermark data.
 48. The integrated circuitas claimed in claim 43, if a data sequence which is embedded as saiddigital watermark data is modulated by a pseudo-random sequence, saidintegrated circuit further comprising: means for demodulating said bitsequence by said pseudo-random sequence; and means for reconstitutingdigital watermark data from said demodulated bit sequence.
 49. Theintegrated circuit as claimed in claim 43, if a data sequence which isembedded as said digital watermark data is modulated by a pseudo-randomsequence, said integrated circuit further comprising: means forobtaining a binary distribution function F(x) which represents aprobability that a number x of ‘1’ bits or ‘0’ bits are included in abit sequence which is read at random from digital data contents, saidbinary distribution function F(x) being obtained by using a probabilityq of reading ‘1’ or ‘0’ in said bit sequence and a repeating number ofembedding each bit of digital watermark data; means for reading an ithdigital watermark sequence of said digital watermark data from a digitalwatermark area of said digital data contents; means for demodulatingsaid digital watermark sequence by said pseudo-random sequence; meansfor assigning ½ to said probability q; means for obtaining a maximumnumber x₀ which satisfies 0≦F(x=x₀)≦1−α and a minimum number x₁ whichsatisfies α≦F(x=x₁)≦1, α being a threshold of reliability of digitalwatermark data which is read; and means for obtaining the number k_(i)of ‘1’ or ‘0’ included in said ith digital watermark sequence; means forreconstituting ith digital watermark data w_(i) as ‘0’ or ‘1’ ifk_(i)≦x₀, and, reconstituting said ith digital watermark data w_(i) as‘1’ or ‘0’ if k_(i)≧x₁.
 50. The integrated circuit as claimed in claim43, if a data sequence which is embedded as said digital watermark datais modulated by a pseudo-random sequence, said integrated circuitfurther comprising: means for obtaining a binary distribution functionF(x) which represents a probability that a number x of ‘1’ bits or ‘0’bits are included in a bit sequence which is read at random from digitaldata contents, said binary distribution function F(x) being obtained byusing a probability q of reading ‘1’ or ‘0’ in said bit sequence and arepeating number t of embedding each bit of digital watermark data;means for reading an ith digital watermark sequence of said digitalwatermark data from a digital watermark area of said digital datacontents; means for demodulating said digital watermark sequence by saidpseudo-random sequence; means for assigning ½ to said probability q;means for obtaining x₀ or x₁ which satisfies 0≦F(x=x₀)≦1−α orα≦F(x=x₁)≦1, α being a threshold of reliability of digital watermarkdata which is read; means for determining whether a value is equal to orless than x₀ or equal to or more than x₁, said value being a mean valueof absolute values of a difference between the number of ‘0’ or ‘1’included in said ith digital watermark sequence and a central value q×tof a binary distribution; means for reconstituting digital watermarkdata by performing majority decision processing for said ith digitalwatermark sequence if said value is equal to or less than x₀ or equal toor more than x₁; and means for determining that there is no digitalwatermark data or the presence is unknown if said value is not equal toor less than x₀ or equal to or more than x₁.
 51. The integrated circuitas claimed in claim 50, further comprising: means for calculating avalue of said binary distribution function F(z), z being said mean valueobtained from the number of ‘0’ or ‘1’ included in said ith digitalwatermark sequence and said central value q×t; and means for outputtingsaid value of F(z) as reliability of digital watermark data.
 52. Acomputer readable medium storing program code for causing a computersystem to read digital watermark data embedded in digital data contents,said computer readable medium comprising: program code means forreceiving said digital data contents; program code means for reading abit sequence from said digital data contents; program code means forcalculating a probability of reading a bit ‘1’ or a bit ‘0’ in said bitsequence by using a test method on the basis of binary distribution;program code means for determining the presence or absence of digitalwatermark data according to said probability; and program code means forreconstituting and generating said digital watermark data from said bitsequence.
 53. The computer readable medium as claimed in claim 52,further comprising: program code means for obtaining a binarydistribution function F(x) which represents a probability that a numberx of ‘1’ bits or ‘0’ bits are included in a bit sequence which is readat random from digital data contents, said binary distribution functionF(x) being obtained by using a probability q of reading ‘1’ or ‘0’ insaid bit sequence and a repeating number of embedding each bit ofdigital watermark data; program code means for reading an ith digitalwatermark sequence of said digital watermark data from a digitalwatermark area of said digital data contents; program code means forcalculating the number k_(i) of ‘1’ or ‘0’ included in said digitalwatermark sequence; and program code means for calculating a probabilityF(k_(i)) by using said binary distribution function F(x); program codemeans for reconstituting ‘1’ or ‘0’ from ith digital watermark dataw_(i) if F(k_(i))>α, reconstituting ‘0’ or ‘1’ from ith digitalwatermark data w_(i) if 1−F(k_(i))>α, and, determining that there is nowatermark data or the presence is unknown if both of F(k_(i))>α and1−F(k_(i))>α are not satisfied, α being a threshold of reliability ofdigital watermark data which is read.
 54. The computer readable mediumas claimed in claim 53, further comprising: program code means foroutputting F(k_(i)) as reliability if said reconstituted digitalwatermark data w_(i) is ‘1’; and program code means for outputting1−F(k_(i)) as reliability if said reconstituted digital watermark dataw_(i) is ‘0’.
 55. The computer readable medium as claimed in claim 52,further comprising: program code means for obtaining a binarydistribution function F(x) which represents a probability that a numberx of ‘1’ bits or ‘0’ bits are included in a bit sequence which is readat random from digital data contents, said binary distribution functionF(x) being obtained by using a probability q of reading ‘1’ or ‘0’ insaid bit sequence and a repeating number of embedding each bit ofdigital watermark data; program code means for reading an ith digitalwatermark sequence of said digital watermark data from a digitalwatermark area of said digital data contents; program code means forchecking whether a probability that said digital watermark sequence isdigital watermark data exceeds said threshold α by using said binarydistribution function F(x), α being a threshold of reliability ofdigital watermark data which is read; and program code means forreconstituting and generating digital watermark data from said digitalwatermark sequence by using majority decision processing if saidprobability exceeds α, and determining that there is no watermark dataor the presence is unknown if said probability does not exceed α. 56.The computer readable medium as claimed in claim 55, further comprisingprogram code means for outputting said probability that said digitalwatermark sequence is digital watermark data as reliability of saidreconstituted digital watermark data.
 57. The computer readable mediumas claimed in claim 52, if a data sequence which is embedded as saiddigital watermark data is modulated by a pseudo-random sequence, saidcomputer readable medium further comprising: program code means fordemodulating said bit sequence by said pseudo-random sequence; andprogram code means for reconstituting digital watermark data from saiddemodulated bit sequence.
 58. The computer readable medium as claimed inclaim 52, if data sequence which is embedded as said digital watermarkdata is modulated by a pseudo-random sequence, said computer readablemedium further comprising: program code means for obtaining a binarydistribution function F(x) which represents a probability that a numberx of ‘1’ bits or ‘0’ bits are included in a bit sequence which is readat random from digital data contents, said binary distribution functionF(x) being obtained by using a probability q of reading ‘1’ or ‘0’ insaid bit sequence and a repeating number of embedding each bit ofdigital watermark data; program code means for reading an ith digitalwatermark sequence of said digital watermark data from a digitalwatermark area of said digital data contents; program code means fordemodulating said digital watermark sequence by said pseudo-randomsequence; program code means for assigning ½ to said probability q;program code means for obtaining a maximum number x₀ which satisfies0≦F(x=x₀)≦1−α and a minimum number x₁ which satisfies α≦F(x=x₁)≦1, αbeing a threshold of reliability of digital watermark data which isread; program code means for obtaining the number k_(i) of ‘1’ or ‘0’included in said ith digital watermark sequence; and program code meansfor reconstituting ith digital watermark data w_(i) as ‘0’ or ‘1’ ifk_(i)≦x₀, and reconstituting said ith digital watermark data w_(i) as‘1’ or ‘0’ if k_(i)≧x₁.
 59. The computer readable medium as claimed inclaim 52, if a data sequence which is embedded as said digital watermarkdata is modulated by a pseudo-random sequence, said computer readablemedium further comprising: program code means for obtaining a binarydistribution function F(x) which represents a probability that a numberx of ‘1’ bits or ‘0’ bits are included in a bit sequence which is readat random from digital data contents, said binary distribution functionF(x) being obtained by using a probability q of reading ‘1’ or ‘0’ insaid bit sequence and a repeating number t of embedding each bit ofdigital watermark data; program code means for reading an ith digitalwatermark sequence of said digital watermark data from a digitalwatermark area of said digital data contents; program code means fordemodulating said digital watermark sequence by said pseudo-randomsequence; program code means for assigning ½ to said probability q;program code means for obtaining x₀ or x₁ which satisfies 0≦F(x=x₀)≦1−αor α≦F(x=x₁)≦1, α being a threshold of reliability of digital watermarkdata which is read; program code means for determining whether a valueis equal to or less than x₀ or equal to or more than x₁, said valuebeing a mean value of absolute values of a difference between the numberof ‘0’ or ‘1’ included in said ith digital watermark sequence and acentral value q×t of a binary distribution; program code means forreconstituting digital watermark data by performing majority decisionprocessing for said ith digital watermark sequence if said value isequal to or less than x₀ or equal to or more than x₁; and program codemeans for determining that there is no digital watermark data or thepresence is unknown if said value is not equal to or less than x₀ orequal to or more than x₁.
 60. The computer readable medium as claimed inclaim 59, further comprising: program code means for calculating a valueof said binary distribution function F(z), z being said mean valueobtained from the number of ‘0’ or ‘1’ included in said ith digitalwatermark sequence and said central value q×t; and program code meansfor outputting said value of F(z) as reliability of digital watermarkdata.
 61. A method for reading digital watermark data from digital datacontents in which each bit of digital watermark data is embedded aplurality of times, said method comprising the steps of: receivingdigital data contents; reading a digital watermark sequence from saiddigital data contents; performing soft decision in code theory byassigning weights to said digital watermark sequence with a weightingfunction; and reconstituting and generating digital watermark data fromsaid digital watermark sequence.
 62. The method as claimed in claim 61,wherein said weighting function is a distribution function obtained by amethod comprising the steps of: dividing first digital data contentsinto one or a plurality of first block data; dividing second digitaldata contents into one or a plurality of second block data, said seconddigital data contents being obtained by manipulating said first digitaldata contents with a predetermined manipulation method; transformingsaid first block data and said second block data into first frequencycoefficients and second frequency coefficients respectively by applyingan orthogonal transform; and obtaining a distribution of differencevalues between said first frequency coefficients and said secondfrequency coefficients, said distribution function being anapproximation of said distribution, wherein said weights are assigned tosaid digital watermark sequence according to values of said distributionfunction.
 63. The method as claimed in claim 61, wherein said weightingfunction is a distribution function obtained by a method comprising thesteps of: dividing first digital data contents into one or a pluralityof first block data; dividing second digital data contents into one or aplurality of second block data, said second digital data contents beingobtained by manipulating said first digital data contents with apredetermined manipulation method; transforming said first block dataand said second block data into first frequency coefficients and secondfrequency coefficients respectively by applying an orthogonal transform;and obtaining said distribution function on the basis of a theory if adistribution of difference values between said first frequencycoefficients and said second frequency coefficients can be obtained bysaid theory, wherein said weights are assigned to said digital watermarksequence according to values of said distribution function.
 64. Anapparatus for reading digital watermark data from digital data contentsin which each bit of digital watermark data is embedded a plurality oftimes, said apparatus comprising: means for receiving digital datacontents; means for reading a digital watermark sequence from saiddigital data contents; means for performing soft decision in code theoryby assigning weights to said digital watermark sequence with a weightingfunction; and means for reconstituting and generating digital watermarkdata from said digital watermark sequence.
 65. The apparatus as claimedin claim 64, wherein said weighting function is a distribution functionobtained by means comprising: means for dividing first digital datacontents into one or a plurality of first block data; means for dividingsecond digital data contents into one or a plurality of second blockdata, said second digital data contents being obtained by manipulatingsaid first digital data contents with a predetermined manipulationmethod; means for transforming said first block data and said secondblock data into first frequency coefficients and second frequencycoefficients respectively by applying an orthogonal transform; and meansfor obtaining a distribution of difference values between said firstfrequency coefficients and said second frequency coefficients, saiddistribution function being an approximation of said distribution,wherein said weights are assigned to said digital watermark sequenceaccording to values of said distribution function.
 66. The apparatus asclaimed in claim 64, wherein said weighting function is a distributionfunction obtained by means comprising: means for dividing first digitaldata contents into one or a plurality of first block data; means fordividing second digital data contents into one or a plurality of secondblock data, said second digital data contents being obtained bymanipulating said first digital data contents with a predeterminedmanipulation method; means for transforming said first block data andsaid second block data into first frequency coefficients and secondfrequency coefficients respectively by applying an orthogonal transform;means for obtaining said distribution function on the basis of a theoryif a distribution of difference values between said first frequencycoefficients and said second frequency coefficients can be obtained bysaid theory, and wherein said weights are assigned to said digitalwatermark sequence according to values of said distribution function.67. An integrated circuit for reading digital watermark data fromdigital data contents in which each bit of digital watermark data isembedded a plurality of times, said integrated circuit comprising: meansfor receiving digital data contents; means for reading a digitalwatermark sequence from said digital data contents; means for performingsoft decision in code theory by assigning weights to said digitalwatermark sequence with a weighting function; and means forreconstituting and generating digital watermark data from said digitalwatermark sequence.
 68. The integrated circuit as claimed in claim 67,wherein said weighting function is a distribution function obtained bymeans comprising: means for dividing first digital data contents intoone or a plurality of first block data; means for dividing seconddigital data contents into one or a plurality of second block data, saidsecond digital data contents being obtained by manipulating said firstdigital data contents with a predetermined manipulation method; meansfor transforming said first block data and said second block data intofirst frequency coefficients and second frequency coefficientsrespectively by applying an orthogonal transform; and means forobtaining a distribution of difference values between said firstfrequency coefficients and said second frequency coefficients, saiddistribution function being an approximation of said distribution,wherein said weights are assigned to said digital watermark sequenceaccording to values of said distribution function.
 69. The integratedcircuit as claimed in claim 67, wherein said weighting function is adistribution function obtained by means comprising: means for dividingfirst digital data contents into one or a plurality of first block data;means for dividing second digital data contents into one or a pluralityof second block data, said second digital data contents being obtainedby manipulating said first digital data contents with a predeterminedmanipulation method; means for transforming said first block data andsaid second block data into first frequency coefficients and secondfrequency coefficients respectively by applying an orthogonal transform;and means for obtaining said distribution function on the basis of atheory if a distribution of difference values between said firstfrequency coefficients and said second frequency coefficients can beobtained by said theory, wherein said weights are assigned to saiddigital watermark sequence according to values of said distributionfunction.
 70. A computer readable medium storing program code forcausing a computer system to read digital watermark data from digitaldata contents in which each bit of digital watermark data is embedded aplurality of times, said computer readable medium comprising: programcode means for receiving digital data contents; program code means forreading a digital watermark sequence from said digital data contents;program code means for performing soft decision in code theory byassigning weights to said digital watermark sequence with a weightingfunction; and program code means for reconstituting and generatingdigital watermark data from said digital watermark sequence.
 71. Thecomputer readable medium as claimed in claim 70, wherein said weightingfunction is a distribution function obtained by program code meanscomprising: program code means for dividing first digital data contentsinto one or a plurality of first block data; program code means fordividing second digital data contents into one or a plurality of secondblock data, said second digital data contents being obtained bymanipulating said first digital data contents with a predeterminedmanipulation method; program code means for transforming said firstblock data and said second block data into first frequency coefficientsand second frequency coefficients respectively by applying an orthogonaltransform; and program code means for obtaining a distribution ofdifference values between said first frequency coefficients and saidsecond frequency coefficients, said distribution function being anapproximation of said distribution, wherein said weights are assigned tosaid digital watermark sequence according to values of said distributionfunction.
 72. The computer readable medium as claimed in claim 70,wherein said weighting function is a distribution function obtained byprogram code means comprising: program code means for dividing firstdigital data contents into one or a plurality of first block data;program code means for dividing second digital data contents into one ora plurality of second block data, said second digital data contentsbeing obtained by manipulating said first digital data contents with apredetermined manipulation method; program code means for transformingsaid first block data and said second block data into first frequencycoefficients and second frequency coefficients respectively by applyingan orthogonal transform; and program code means for obtaining saiddistribution function on the basis of a theory if a distribution ofdifference values between said first frequency coefficients and saidsecond frequency coefficients can be obtained by said theory, whereinsaid weights are assigned to said digital watermark sequence accordingto values of said distribution function.